[Qemu-devel] [PATCH] tcg-i386: Remove abort from GETPC_LDST

[Richard Henderson <rth@twiddle.net>]

Indeed, remove it entirely and remove the is_tcg_gen_code check
from GETPC_EXT.

Fixes https://bugs.launchpad.net/qemu/+bug/1218098 wherein a call
to a "normal" helper function performed a sequence of tail calls
all the way into the memory helper functions, leading to a stack
frame in which the memory helper function appeared to be called
directly from tcg.

Signed-off-by: Richard Henderson <rth@twiddle.net>
---
 include/exec/exec-all.h | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

This is actually conclusive proof that using is_tcg_gen_code, and
thus any scheme that requires GETPC_LDST, is fundamentally flawed.

Thankfully, the follow-up patch sets that I've already posted give
a framework for properly fixing this.  I've already posted a cleanup
for ARM to fix this.  I have pending but unposted patch sets for
AArch64 and PowerPC.

In the meantime, please apply this fix for x86_64 asap.


r~



diff --git a/include/exec/exec-all.h b/include/exec/exec-all.h
index b70028a..ffb69a4 100644
--- a/include/exec/exec-all.h
+++ b/include/exec/exec-all.h
@@ -326,9 +326,7 @@ extern uintptr_t tci_tb_ptr;
    (6) jump to corresponding code of the next of fast path
  */
 # if defined(__i386__) || defined(__x86_64__)
-#  define GETRA() ((uintptr_t)__builtin_return_address(0))
-/* The return address argument for ldst is passed directly.  */
-#  define GETPC_LDST()  (abort(), 0)
+#  define GETPC_EXT()  GETPC()
 # elif defined (_ARCH_PPC) && !defined (_ARCH_PPC64)
 #  define GETRA() ((uintptr_t)__builtin_return_address(0))
 #  define GETPC_LDST() ((uintptr_t) ((*(int32_t *)(GETRA() - 4)) - 1))
@@ -349,7 +347,7 @@ static inline uintptr_t tcg_getpc_ldst(uintptr_t ra)
                                    not the start of the next opcode  */
     return ra;
 }
-#elif defined(__aarch64__)
+# elif defined(__aarch64__)
 #  define GETRA()       ((uintptr_t)__builtin_return_address(0))
 #  define GETPC_LDST()  tcg_getpc_ldst(GETRA())
 static inline uintptr_t tcg_getpc_ldst(uintptr_t ra)
@@ -367,7 +365,9 @@ static inline uintptr_t tcg_getpc_ldst(uintptr_t ra)
 #  error "CONFIG_QEMU_LDST_OPTIMIZATION needs GETPC_LDST() implementation!"
 # endif
 bool is_tcg_gen_code(uintptr_t pc_ptr);
-# define GETPC_EXT() (is_tcg_gen_code(GETRA()) ? GETPC_LDST() : GETPC())
+# ifndef GETPC_EXT
+#  define GETPC_EXT() (is_tcg_gen_code(GETRA()) ? GETPC_LDST() : GETPC())
+# endif
 #else
 # define GETPC_EXT() GETPC()
 #endif
-- 
1.8.1.4