diff options
Diffstat (limited to 'pp.h')
| -rw-r--r-- | pp.h | 47 |
1 files changed, 38 insertions, 9 deletions
@@ -283,29 +283,58 @@ Does not use C<TARG>. See also C<L</XPUSHu>>, C<L</mPUSHu>> and C<L</PUSHu>>. =cut */ +/* _EXTEND_SAFE_N(n): private helper macro for EXTEND(). + * Tests whether the value of n would be truncated when implicitly cast to + * SSize_t as an arg to stack_grow(). If so, sets it to -1 instead to + * trigger a panic. It will be constant folded on platforms where this + * can't happen. + */ + +#define _EXTEND_SAFE_N(n) \ + (sizeof(n) > sizeof(SSize_t) && ((SSize_t)(n) != (n)) ? -1 : (n)) + #ifdef STRESS_REALLOC # define EXTEND(p,n) STMT_START { \ - sp = stack_grow(sp,p,(SSize_t) (n)); \ + sp = stack_grow(sp,p,_EXTEND_SAFE_N(n)); \ PERL_UNUSED_VAR(sp); \ } STMT_END /* Same thing, but update mark register too. */ # define MEXTEND(p,n) STMT_START { \ const SSize_t markoff = mark - PL_stack_base; \ - sp = stack_grow(sp,p,(SSize_t) (n)); \ + sp = stack_grow(sp,p,_EXTEND_SAFE_N(n)); \ mark = PL_stack_base + markoff; \ PERL_UNUSED_VAR(sp); \ } STMT_END #else -# define EXTEND(p,n) STMT_START { \ - if (UNLIKELY(PL_stack_max - p < (SSize_t)(n))) { \ - sp = stack_grow(sp,p,(SSize_t) (n)); \ + +/* _EXTEND_NEEDS_GROW(p,n): private helper macro for EXTEND(). + * Tests to see whether n is too big and we need to grow the stack. Be + * very careful if modifying this. There are many ways to get things wrong + * (wrapping, truncating etc) that could cause a false negative and cause + * the call to stack_grow() to be skipped. On the other hand, false + * positives are safe. + * Bear in mind that sizeof(p) may be less than, equal to, or greater + * than sizeof(n), and while n is documented to be signed, someone might + * pass an unsigned value or expression. In general don't use casts to + * avoid warnings; instead expect the caller to fix their code. + * It is legal for p to be greater than PL_stack_max. + * If the allocated stack is already very large but current usage is + * small, then PL_stack_max - p might wrap round to a negative value, but + * this just gives a safe false positive + */ + +# define _EXTEND_NEEDS_GROW(p,n) ( (n) < 0 || PL_stack_max - p < (n)) + +# define EXTEND(p,n) STMT_START { \ + if (UNLIKELY(_EXTEND_NEEDS_GROW(p,n))) { \ + sp = stack_grow(sp,p,_EXTEND_SAFE_N(n)); \ PERL_UNUSED_VAR(sp); \ } } STMT_END /* Same thing, but update mark register too. */ -# define MEXTEND(p,n) STMT_START { \ - if (UNLIKELY(PL_stack_max - p < (SSize_t)(n))) { \ - const SSize_t markoff = mark - PL_stack_base; \ - sp = stack_grow(sp,p,(SSize_t) (n)); \ +# define MEXTEND(p,n) STMT_START { \ + if (UNLIKELY(_EXTEND_NEEDS_GROW(p,n))) { \ + const SSize_t markoff = mark - PL_stack_base;\ + sp = stack_grow(sp,p,_EXTEND_SAFE_N(n)); \ mark = PL_stack_base + markoff; \ PERL_UNUSED_VAR(sp); \ } } STMT_END |