diff options
Diffstat (limited to 'gcc/explow.c')
| -rw-r--r-- | gcc/explow.c | 20 |
1 files changed, 12 insertions, 8 deletions
diff --git a/gcc/explow.c b/gcc/explow.c index 15c9cfb..0fbc6d2 100644 --- a/gcc/explow.c +++ b/gcc/explow.c @@ -1293,9 +1293,9 @@ get_dynamic_stack_size (rtx *psize, unsigned size_align, /* Return the number of bytes to "protect" on the stack for -fstack-check. - "protect" in the context of -fstack-check means how many bytes we - should always ensure are available on the stack. More importantly - this is how many bytes are skipped when probing the stack. + "protect" in the context of -fstack-check means how many bytes we need + to always ensure are available on the stack; as a consequence, this is + also how many bytes are first skipped when probing the stack. On some targets we want to reuse the -fstack-check prologue support to give a degree of protection against stack clashing style attacks. @@ -1303,14 +1303,16 @@ get_dynamic_stack_size (rtx *psize, unsigned size_align, In that scenario we do not want to skip bytes before probing as that would render the stack clash protections useless. - So we never use STACK_CHECK_PROTECT directly. Instead we indirect though - this helper which allows us to provide different values for - -fstack-check and -fstack-clash-protection. */ + So we never use STACK_CHECK_PROTECT directly. Instead we indirectly + use it through this helper, which allows to provide different values + for -fstack-check and -fstack-clash-protection. */ + HOST_WIDE_INT get_stack_check_protect (void) { if (flag_stack_clash_protection) return 0; + return STACK_CHECK_PROTECT; } @@ -1532,6 +1534,8 @@ allocate_dynamic_stack_space (rtx size, unsigned size_align, saved_stack_pointer_delta = stack_pointer_delta; + /* If stack checking or stack clash protection is requested, + then probe the stack while allocating space from it. */ if (flag_stack_check && STACK_CHECK_MOVING_SP) anti_adjust_stack_and_probe (size, false); else if (flag_stack_clash_protection) @@ -1940,8 +1944,8 @@ emit_stack_clash_protection_probe_loop_end (rtx loop_lab, rtx end_loop, probes were not emitted. 2. It never skips probes, whereas anti_adjust_stack_and_probe will - skip probes on the first couple PROBE_INTERVALs on the assumption - they're done elsewhere. + skip the probe on the first PROBE_INTERVAL on the assumption it + was already done in the prologue and in previous allocations. 3. It only allocates and probes SIZE bytes, it does not need to allocate/probe beyond that because this probing style does not |