https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98692
--- Comment #18 from Mark Wielaard <mark at gcc dot gnu.org> ---
The current thinking (Julian did the thinking, I am just repeating) is that
this is caused by the way the _savegpr and/or restgpr functions return using
blr.
PPC has two special "lets zap the red zone" (the 288 bytes below the stack
pointer) cases:
# define VG_STACK_REDZONE_SZB 288 // number of addressable bytes below R1
// from 64-bit PowerPC ELF ABI
// Supplement 1.7
guest_ppc_zap_RZ_at_blr
guest is ppc64-linux ==> True
guest is ppc32-linux ==> False
guest is other ==> inapplicable
guest_ppc_zap_RZ_at_bl
guest is ppc64-linux ==> const True
guest is ppc32-linux ==> const False
guest is other ==> inapplicable
guest_stack_redzone_size
guest is ppc32-linux ==> 0
guest is ppc64-linux ==> 288
guest is amd64-linux ==> 128
guest is other ==> inapplicable
/* PPC and AMD64 GUESTS only: how many bytes below the
stack pointer are validly addressible? */
Int guest_stack_redzone_size;
/* PPC GUESTS only: should we zap the stack red zone at a 'blr'
(function return) ? */
Bool guest_ppc_zap_RZ_at_blr;
/* PPC GUESTS only: should we zap the stack red zone at a 'bl'
(function call) ? Is supplied with the guest address of the
target of the call since that may be significant. If NULL,
is assumed equivalent to a fn which always returns False. */
Bool (*guest_ppc_zap_RZ_at_bl)(Addr);
# if defined(VGP_ppc32_linux)
vex_abiinfo.guest_ppc_zap_RZ_at_blr = False;
vex_abiinfo.guest_ppc_zap_RZ_at_bl = NULL;
# endif
# if defined(VGP_ppc64be_linux)
vex_abiinfo.guest_ppc_zap_RZ_at_blr = True;
vex_abiinfo.guest_ppc_zap_RZ_at_bl = const_True;
vex_abiinfo.host_ppc_calls_use_fndescrs = True;
# endif
# if defined(VGP_ppc64le_linux)
vex_abiinfo.guest_ppc_zap_RZ_at_blr = True;
vex_abiinfo.guest_ppc_zap_RZ_at_bl = const_True;
vex_abiinfo.host_ppc_calls_use_fndescrs = False;
# endif
What happens on a blr function return is that, based on the
guest_ppc_zap_RZ_at_blr value, the redzone is marked as containing undefined
values.
And indeed, with this patch:
diff --git a/coregrind/m_translate.c b/coregrind/m_translate.c
index 332202a91..6dd01afac 100644
--- a/coregrind/m_translate.c
+++ b/coregrind/m_translate.c
@@ -1709,7 +1709,7 @@ Bool VG_(translate) ( ThreadId tid,
# endif
# if defined(VGP_ppc64le_linux)
- vex_abiinfo.guest_ppc_zap_RZ_at_blr = True;
+ vex_abiinfo.guest_ppc_zap_RZ_at_blr = False;
vex_abiinfo.guest_ppc_zap_RZ_at_bl = const_True;
vex_abiinfo.host_ppc_calls_use_fndescrs = False;
# endif
The warning goes away.
But is that the right thing to do always? It seems to mask issues where a
function is using the red zone values set by another function.
