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[PATCH 1/1] target/ppc: fix ELFv2 signal handler endianness


From: Vincent Fazio
Subject: [PATCH 1/1] target/ppc: fix ELFv2 signal handler endianness
Date: Sun, 15 Mar 2020 10:52:02 -0500

From: Vincent Fazio <address@hidden>

In ELFv2, function pointers are entry points and are in host endianness.

Previously, the signal handler would be swapped if the target CPU was a
different endianness than the host. This would cause a SIGSEGV when
attempting to translate the opcode pointed to by the swapped address.

 Thread 1 "qemu-ppc64" received signal SIGSEGV, Segmentation fault.
 0x00000000600a9257 in ldl_he_p (ptr=0x4c2c061000000000) at 
qemu/include/qemu/bswap.h:351
 351        __builtin_memcpy(&r, ptr, sizeof(r));

 #0  0x00000000600a9257 in ldl_he_p (ptr=0x4c2c061000000000) at 
qemu/include/qemu/bswap.h:351
 #1  0x00000000600a92fe in ldl_be_p (ptr=0x4c2c061000000000) at 
qemu/include/qemu/bswap.h:449
 #2  0x00000000600c0790 in translator_ldl_swap at 
qemu/include/exec/translator.h:201
 #3  0x000000006011c1ab in ppc_tr_translate_insn at 
qemu/target/ppc/translate.c:7856
 #4  0x000000006005ae70 in translator_loop at qemu/accel/tcg/translator.c:102

Now, no swap is performed and execution continues properly.

Signed-off-by: Vincent Fazio <address@hidden>
---
 linux-user/ppc/signal.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/linux-user/ppc/signal.c b/linux-user/ppc/signal.c
index 5b82af6cb6..c7f6455170 100644
--- a/linux-user/ppc/signal.c
+++ b/linux-user/ppc/signal.c
@@ -567,9 +567,13 @@ void setup_rt_frame(int sig, struct target_sigaction *ka,
         env->nip = tswapl(handler->entry);
         env->gpr[2] = tswapl(handler->toc);
     } else {
-        /* ELFv2 PPC64 function pointers are entry points, but R12
-         * must also be set */
-        env->nip = tswapl((target_ulong) ka->_sa_handler);
+        /*
+         * ELFv2 PPC64 function pointers are entry points and are in host
+         * endianness so should not to be swapped.
+         *
+         * Note: R12 must also be set.
+         */
+        env->nip = (target_ulong) ka->_sa_handler;
         env->gpr[12] = env->nip;
     }
 #else
-- 
2.25.1




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