{"id":2224132,"url":"http://patchwork.ozlabs.org/api/patches/2224132/?format=json","web_url":"http://patchwork.ozlabs.org/project/qemu-devel/patch/20260416182527.3862296-1-mattst88@gmail.com/","project":{"id":14,"url":"http://patchwork.ozlabs.org/api/projects/14/?format=json","name":"QEMU Development","link_name":"qemu-devel","list_id":"qemu-devel.nongnu.org","list_email":"qemu-devel@nongnu.org","web_url":"","scm_url":"","webscm_url":"","list_archive_url":"","list_archive_url_format":"","commit_url_format":""},"msgid":"<20260416182527.3862296-1-mattst88@gmail.com>","list_archive_url":null,"date":"2026-04-16T18:25:27","name":"linux-user/ppc: Fix ppc64 rt_sigframe stack offset","commit_ref":null,"pull_url":null,"state":"new","archived":false,"hash":"2d21272ea9d5c0b0abab7e9167fc412e43da566c","submitter":{"id":7917,"url":"http://patchwork.ozlabs.org/api/people/7917/?format=json","name":"Matt Turner","email":"mattst88@gmail.com"},"delegate":null,"mbox":"http://patchwork.ozlabs.org/project/qemu-devel/patch/20260416182527.3862296-1-mattst88@gmail.com/mbox/","series":[{"id":500211,"url":"http://patchwork.ozlabs.org/api/series/500211/?format=json","web_url":"http://patchwork.ozlabs.org/project/qemu-devel/list/?series=500211","date":"2026-04-16T18:25:27","name":"linux-user/ppc: Fix ppc64 rt_sigframe stack offset","version":1,"mbox":"http://patchwork.ozlabs.org/series/500211/mbox/"}],"comments":"http://patchwork.ozlabs.org/api/patches/2224132/comments/","check":"pending","checks":"http://patchwork.ozlabs.org/api/patches/2224132/checks/","tags":{},"related":[],"headers":{"Return-Path":"","X-Original-To":"incoming@patchwork.ozlabs.org","Delivered-To":"patchwork-incoming@legolas.ozlabs.org","Authentication-Results":["legolas.ozlabs.org;\n\tdkim=pass (2048-bit key;\n unprotected) header.d=gmail.com header.i=@gmail.com header.a=rsa-sha256\n header.s=20251104 header.b=mrrPaxQx;\n\tdkim-atps=neutral","legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=nongnu.org\n (client-ip=209.51.188.17; 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helo=mail-yw1-x112d.google.com","X-Spam_score_int":"-17","X-Spam_score":"-1.8","X-Spam_bar":"-","X-Spam_report":"(-1.8 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1,\n DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1,\n FREEMAIL_ENVFROM_END_DIGIT=0.25, FREEMAIL_FROM=0.001,\n RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001,\n SPF_PASS=-0.001 autolearn=ham autolearn_force=no","X-Spam_action":"no action","X-Mailman-Approved-At":"Thu, 16 Apr 2026 18:37:49 -0400","X-BeenThere":"qemu-devel@nongnu.org","X-Mailman-Version":"2.1.29","Precedence":"list","List-Id":"qemu development ","List-Unsubscribe":",\n ","List-Archive":"","List-Post":"","List-Help":"","List-Subscribe":",\n ","Errors-To":"qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org","Sender":"qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org"},"content":"The kernel's 64-bit signal delivery (signal_64.c) uses:\n\n newsp = frame - __SIGNAL_FRAMESIZE\n\nwhile the 32-bit path (signal_32.c) uses:\n\n newsp = frame - (__SIGNAL_FRAMESIZE + 16)\n\nThe extra 16 bytes in the 32-bit case is to place siginfo and ucontext\nat the same offsets as older kernels (see the comment in signal_32.c).\nThe 64-bit rt_sigframe starts with ucontext directly and does not need\nthis adjustment.\n\nQEMU's setup_rt_frame() unconditionally used (SIGNAL_FRAMESIZE + 16)\nfor both 32-bit and 64-bit, placing the handler's SP 16 bytes too low\non ppc64. Signal delivery and return still worked because do_rt_sigreturn\nhad the matching wrong offset, but the vDSO DWARF unwind info encodes\nthe correct kernel offset. This caused any DWARF unwinder (libunwind,\nlibgcc, etc.) to compute a CFA that is 16 bytes off, reading garbage\nregister values from the signal frame.\n\nDefine RT_SIGFRAME_ADJUST (0 on ppc64, 16 on ppc32) and use it in both\nsetup_rt_frame and do_rt_sigreturn to match the kernel.\n\nThis was verified by A/B testing with libunwind's test suite:\n\n ppc64le: Gtest-bt, Ltest-bt, Gtest-concurrent, Ltest-concurrent,\n and Ltest-sig-context all change from FAIL to PASS.\n ppc64be: Gtest-bt, Ltest-bt, and Ltest-sig-context all change\n from FAIL to PASS.\n\nSigned-off-by: Matt Turner \n---\n linux-user/ppc/signal.c | 16 ++++++++++++++--\n 1 file changed, 14 insertions(+), 2 deletions(-)","diff":"diff --git ./linux-user/ppc/signal.c ./linux-user/ppc/signal.c\nindex 24e5a02a78..a9c10e0987 100644\n--- ./linux-user/ppc/signal.c\n+++ ./linux-user/ppc/signal.c\n@@ -210,6 +210,18 @@ QEMU_BUILD_BUG_ON(offsetof(struct target_rt_sigframe, uc.tuc_mcontext)\n \n #endif\n \n+#ifdef TARGET_PPC64\n+#define RT_SIGFRAME_ADJUST 0\n+#else\n+/*\n+ * For 32-bit rt sigframes we have an extra 16 bytes of gap\n+ * on top of __SIGNAL_FRAMESIZE; this is to get the siginfo\n+ * and ucontext in the same positions as in older kernels.\n+ * See Linux's arch/powerpc/kernel/signal_32.c.\n+ */\n+#define RT_SIGFRAME_ADJUST 16\n+#endif\n+\n #if defined(TARGET_PPC64)\n \n struct target_func_ptr {\n@@ -525,7 +537,7 @@ void setup_rt_frame(int sig, struct target_sigaction *ka,\n env->fpscr = 0;\n \n /* Create a stack frame for the caller of the handler. */\n- newsp = rt_sf_addr - (SIGNAL_FRAMESIZE + 16);\n+ newsp = rt_sf_addr - (SIGNAL_FRAMESIZE + RT_SIGFRAME_ADJUST);\n err |= put_user(env->gpr[1], newsp, target_ulong);\n \n if (err)\n@@ -641,7 +653,7 @@ long do_rt_sigreturn(CPUPPCState *env)\n struct target_rt_sigframe *rt_sf = NULL;\n target_ulong rt_sf_addr;\n \n- rt_sf_addr = env->gpr[1] + SIGNAL_FRAMESIZE + 16;\n+ rt_sf_addr = env->gpr[1] + SIGNAL_FRAMESIZE + RT_SIGFRAME_ADJUST;\n if (!lock_user_struct(VERIFY_READ, rt_sf, rt_sf_addr, 1))\n goto sigsegv;\n \n","prefixes":[]}