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bcheck: remove static (compile-time) control
Providing both run-time and compile-time control for bounds checking as an user interface appears unnecessary and confusing. Also: - replace 'bound_...' by 'bounds_...' for consistency - tcc-doc: put related info into one place and cleanup The __bounds_checking(x) function is still missing explanation. (I.e. what happens if the accumulated value drops below zero.)
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grischka
parent
a34a9775ba
commit
f9870f7860
@ -198,7 +198,7 @@ static Tree * splay_delete(size_t addr, Tree *t);
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void splay_printtree(Tree * t, int d);
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/* external interface */
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void __bound_checking (int no_check);
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void __bounds_checking (int no_check);
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void __bound_never_fatal (int no_check);
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DLL_EXPORT void * __bound_ptr_add(void *p, size_t offset);
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DLL_EXPORT void * __bound_ptr_indir1(void *p, size_t offset);
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@ -359,7 +359,7 @@ static void fetch_and_add(int* variable, int value)
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}
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/* enable/disable checking. This can be used in signal handlers. */
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void __bound_checking (int no_check)
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void __bounds_checking (int no_check)
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{
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fetch_and_add (&no_checking, no_check);
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}
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104
tcc-doc.texi
104
tcc-doc.texi
@ -351,26 +351,8 @@ invalid pointer} instead of the laconic @code{Segmentation
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fault}.
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@item -b
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Generate additional support code to check
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memory allocations and array/pointer bounds. @option{-g} is implied. Note
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that the generated code is slower and bigger in this case.
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The bound checking code is not included in shared libraries. The main executable should always be compiled with the @option{-b}.
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There are five environment variables that can be used:
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@table @option
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@item TCC_BOUNDS_WARN_POINTER_ADD
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Print warning when pointer add creates an illegal pointer.
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@item TCC_BOUNDS_PRINT_CALLS
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Print bound checking calls. Can be used for debugging.
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@item TCC_BOUNDS_PRINT_HEAP
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Print heap objects that are not freed at exit of program.
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@item TCC_BOUNDS_PRINT_STATISTIC
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Print statistic information at exit of program.
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@item TCC_BOUNDS_NEVER_FATAL
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Try to continue in case of a bound checking error.
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@end table
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Note: @option{-b} is only available on i386 (linux and windows), x86_64 (linux and windows), arm, arm64 and riscv64 for the moment.
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Generate additional support code to check memory allocations and array/pointer
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bounds (@pxref{Bounds}). @option{-g} is implied.
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@item -bt[N]
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Display N callers in stack traces. This is useful with @option{-g} or @option{-b}.
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@ -686,8 +668,6 @@ are supported.
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@item Binary digits can be entered (@code{0b101} instead of
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@code{5}).
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@item @code{__BOUNDS_CHECKING_ON} is defined if bound checking is activated.
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@end itemize
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@node asm
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@ -881,16 +861,7 @@ GROUP ( /lib/libc.so.6 /usr/lib/libc_nonshared.a )
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@cindex bound checks
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@cindex memory checks
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This feature is activated with the @option{-b} (@pxref{Invoke}).
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Note that pointer size is @emph{unchanged} and that code generated
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with bound checks is @emph{fully compatible} with unchecked
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code. When a pointer comes from unchecked code, it is assumed to be
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valid. Even very obscure C code with casts should work correctly.
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For more information about the ideas behind this method, see
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@url{http://www.doc.ic.ac.uk/~phjk/BoundsChecking.html}.
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This feature is activated with the @option{-b} option (@pxref{Invoke}).
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Here are some examples of caught errors:
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@table @asis
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@ -946,41 +917,58 @@ Here are some examples of caught errors:
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free(tab);
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@}
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@end example
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@end table
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Signal handlers are not compatible with bounds checking. The code
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below can be used to protect signal handlers.
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The @code{__attribute__((bound_no_checking))} will prevent all bound checking
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code generation. If a signal handler calls another function this
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function must also use @code{__attribute__((bound_no_checking))}.
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TCC defines @code{__BOUNDS_CHECKING_ON} if activated.
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The fork() function call in a multi threaded application is also a problem.
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To solve this all bounds checking can be disabled by calling
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@code{__bound_checking(1)}. The call to @code{__bound_checking(1)} will disable bounds
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checking in the whole application.
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There are five environment variables that can be used to control the behavior:
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@itemize
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@item TCC_BOUNDS_WARN_POINTER_ADD
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- Print warning when pointer add creates an illegal pointer.
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@item TCC_BOUNDS_PRINT_CALLS
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- Print bound checking calls. Can be used for debugging.
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@item TCC_BOUNDS_PRINT_HEAP
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- Print heap objects that are not freed at exit of program.
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@item TCC_BOUNDS_PRINT_STATISTIC
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- Print statistic information at exit of program.
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@item TCC_BOUNDS_NEVER_FATAL
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- Try to continue in case of a bound checking error.
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@end itemize
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The @code{BOUNDS_CHECKING_OFF} and @code{BOUNDS_CHECKING_ON} can also be used to
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disable bounds checking for some code. This is not recommended.
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It is better to fix the code.
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Also, a function @code{__bounds_checking(x)} can be used to turn off/on bounds
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checking from usercode (see below).
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Notes:
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@itemize
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@item Only available on i386 (linux and windows), x86_64 (linux and windows),
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arm, arm64 and riscv64 for the moment.
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@item The generated code is slower and bigger.
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@item The bound checking code is not included in shared libraries. The main
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executable should always be compiled with the @option{-b}.
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@item Pointer size is @emph{unchanged} and code generated with bound checks is
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@emph{fully compatible} with unchecked code. When a pointer comes from
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unchecked code, it is assumed to be valid. Even very obscure C code with
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casts should work correctly.
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@item Signal handlers are not compatible with bounds checking. The fork()
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function call in a multi threaded application is also a problem.
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The code below can be used to solve this.
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@end itemize
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@example
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#if defined(__TINYC__) && __BOUNDS_CHECKING_ON
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#undef __attribute__
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extern void __bound_checking (int no_check);
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#define BOUNDS_CHECKING_OFF __bound_checking(1)
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#define BOUNDS_CHECKING_ON __bound_checking(-1)
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#define BOUNDS_NO_CHECKING __attribute__((bound_no_checking))
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#ifdef __BOUNDS_CHECKING_ON
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extern void __bounds_checking (int x);
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# define BOUNDS_CHECKING_OFF __bounds_checking(1)
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# define BOUNDS_CHECKING_ON __bounds_checking(-1)
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#else
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#define BOUNDS_CHECKING_OFF
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#define BOUNDS_CHECKING_ON
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#define BOUNDS_NO_CHECKING
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# define BOUNDS_CHECKING_OFF
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# define BOUNDS_CHECKING_ON
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#endif
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void signal_handler(int sig, void *info, void *ucontext) BOUNDS_NO_CHECKING
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void signal_handler(int sig, void *info, void *ucontext)
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@{
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BOUNDS_CHECKING_OFF;
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... signal handler code without generated bounds checking code.
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BOUNDS_CHECKING_ON;
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@}
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void run(const char *cmd)
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@ -999,9 +987,11 @@ void run(const char *cmd)
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break;
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@}
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@}
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@end example
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For more information about the ideas behind this method, see
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@url{http://www.doc.ic.ac.uk/~phjk/BoundsChecking.html}.
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@node Libtcc
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@chapter The @code{libtcc} library
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3
tcc.h
3
tcc.h
@ -505,8 +505,7 @@ struct FuncAttr {
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func_dtor : 1, /* attribute((destructor)) */
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func_args : 8, /* PE __stdcall args */
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func_alwinl : 1, /* always_inline */
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no_bcheck : 1, /* no bound checking */
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xxxx :14;
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xxxx : 15;
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};
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/* symbol management */
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38
tccgen.c
38
tccgen.c
@ -1501,8 +1501,6 @@ static void merge_funcattr(struct FuncAttr *fa, struct FuncAttr *fa1)
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fa->func_ctor = 1;
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if (fa1->func_dtor)
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fa->func_dtor = 1;
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if (fa1->no_bcheck)
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fa->no_bcheck = 1;
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}
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/* Merge attributes. */
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@ -4129,12 +4127,6 @@ redo:
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case TOK_ALWAYS_INLINE2:
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ad->f.func_alwinl = 1;
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break;
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#ifdef CONFIG_TCC_BCHECK
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case TOK_NO_BOUND_CHECK1:
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case TOK_NO_BOUND_CHECK2:
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ad->f.no_bcheck = 1;
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break;
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#endif
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case TOK_SECTION1:
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case TOK_SECTION2:
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skip('(');
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@ -5967,26 +5959,6 @@ special_math_val:
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if (t < TOK_UIDENT)
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expect("identifier");
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s = sym_find(t);
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#ifdef CONFIG_TCC_BCHECK
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/* HACK to undo alias definition in tccpp.c
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if function has no bound checking */
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if (tcc_state->do_bounds_check == 0 && s &&
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(s->type.t & VT_BTYPE) == VT_FUNC && (s->asm_label & SYM_FIELD)) {
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const char *name = get_tok_str(s->asm_label & ~SYM_FIELD, NULL);
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if (name && strncmp (name, "__bound_", strlen("__bound_")) == 0) {
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char str[100];
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int v = s->v;
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sprintf (str, "!%s", name); /* illegal name */
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t = tok_alloc(str, strlen(str))->tok;
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s = sym_find(t);
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if (s == NULL)
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s = external_global_sym(t, &func_old_type);
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s->asm_label = v | SYM_FIELD; /* use old name as alias */
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}
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}
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#endif
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if (!s || IS_ASM_SYM(s)) {
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const char *name = get_tok_str(t, NULL);
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if (tok != '(')
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@ -8122,14 +8094,7 @@ static void decl_initializer_alloc(CType *type, AttributeDef *ad, int r,
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'cur_text_section' */
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static void gen_function(Sym *sym)
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{
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/* Initialize VLA state */
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struct scope f = { 0 };
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#ifdef CONFIG_TCC_BCHECK
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unsigned char save_bcheck = tcc_state->do_bounds_check;
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if (sym->type.ref->f.no_bcheck)
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tcc_state->do_bounds_check = 0;
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#endif
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cur_scope = root_scope = &f;
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nocode_wanted = 0;
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ind = cur_text_section->data_offset;
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@ -8183,9 +8148,6 @@ static void gen_function(Sym *sym)
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check_vstack();
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/* do this after funcend debug info */
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next();
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#ifdef CONFIG_TCC_BCHECK
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tcc_state->do_bounds_check = save_bcheck;
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#endif
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}
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static void gen_inline_functions(TCCState *s)
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4
tcctok.h
4
tcctok.h
@ -134,10 +134,6 @@
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DEF(TOK_DESTRUCTOR2, "__destructor__")
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DEF(TOK_ALWAYS_INLINE1, "always_inline")
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DEF(TOK_ALWAYS_INLINE2, "__always_inline__")
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#ifdef CONFIG_TCC_BCHECK
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DEF(TOK_NO_BOUND_CHECK1, "bound_no_checking")
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DEF(TOK_NO_BOUND_CHECK2, "__bound_no_checking__")
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#endif
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DEF(TOK_MODE, "__mode__")
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DEF(TOK_MODE_QI, "__QI__")
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@ -11,14 +11,12 @@
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/* See tcc-doc.info */
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#if defined(__TINYC__) && __BOUNDS_CHECKING_ON
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#undef __attribute__
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extern void __bound_checking (int no_check);
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#define BOUNDS_CHECKING_OFF __bound_checking(1)
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#define BOUNDS_CHECKING_ON __bound_checking(-1)
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#define BOUNDS_NO_CHECKING __attribute__((bound_no_checking))
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extern void __bounds_checking (int no_check);
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#define BOUNDS_CHECKING_OFF __bounds_checking(1)
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#define BOUNDS_CHECKING_ON __bounds_checking(-1)
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#else
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#define BOUNDS_CHECKING_OFF
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#define BOUNDS_CHECKING_ON
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#define BOUNDS_NO_CHECKING
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#endif
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static volatile int run = 1;
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@ -26,15 +24,16 @@ static int dummy[10];
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static sem_t sem;
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static void
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add (void) BOUNDS_NO_CHECKING
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add (void)
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{
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int i;
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BOUNDS_CHECKING_OFF;
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for (i = 0; i < (sizeof(dummy)/sizeof(dummy[0])); i++) {
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dummy[i]++;
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}
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/* Should not be translated into __bound_memset */
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memset (&dummy[0], 0, sizeof(dummy));
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BOUNDS_CHECKING_ON;
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}
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static void *
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@ -56,10 +55,12 @@ do_signal (void *unused)
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return NULL;
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}
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static void signal_handler(int sig) BOUNDS_NO_CHECKING
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static void signal_handler(int sig)
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{
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BOUNDS_CHECKING_OFF;
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add();
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sem_post (&sem);
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BOUNDS_CHECKING_ON;
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}
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int
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