From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 8B44E47DD72 for ; Wed, 1 Apr 2026 16:16:18 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775060178; cv=none; b=S40d1/XaUov8Sg2WW5qipVzwlx127T2UrdOGnejoIPdcMm2Ec6CzSglKuHPDF1AhB+tcvwllv/WTZYiVO4fYEqeew1+wCLdHZNb1lKbM5t2ksSTTSlnLCsTHh7iTYWhkcvWa4fdkqOvmcz9bZ2H6Ho0nlkIm0N1WIUVDvHo5Ols= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775060178; c=relaxed/simple; bh=KUQJ3hEVIhv7BXiCKAxf5dBYgVqJW04hkPxC2lJicDw=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=o8kobyoi/b+Oe0o1dRn1h4pUgxpn7jOr18Pu8hjrDqlE0wZa1kF4413SEge+EARO3bI8rtSux8WTg82s4FWh+P1Ea4WvTYBBitHgmvNKqpQZu3AmnzuXo1XSX6aDN1sCWwuwtot6aW+SGSqczfJfD3H1rwlpp7KEjwbU86eBpm0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=ZHh80maj; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="ZHh80maj" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 35FE4C19423; Wed, 1 Apr 2026 16:16:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1775060177; bh=KUQJ3hEVIhv7BXiCKAxf5dBYgVqJW04hkPxC2lJicDw=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=ZHh80maj3K8YykzfN2vx1xSlNl8VF3SYNhnWlP3Za2koEXqqd5duA0u4gVBmDyAcU xXH/4nNyF6ORVs8GvYY3V+JtbeTxPFq2u2fls0263VK+hogolSMA2ZqWeeWW9LmXPk 3DAUdVWM6gV8t9ts5yWsu6wRAMffE2f1hprMpmz+WAJ49zJGlHT4XFoNIUcCAnNiL9 6PGyApynivWRpwu1ftbdcP7IWXFRUpsKMxwb+PRuzsvi8ErnR1Y+SNE0mZkOuprb7N 1XzEz/CA4JWaW594BjdhkXiXWkQgvjRwkywEXtuAE7WJ1VehIuAaqEESameL93N7Ul FyJ7qUX3TzbEA== From: Sasha Levin To: stable@vger.kernel.org Cc: Xi Ruoyao , Huacai Chen , Sasha Levin Subject: [PATCH 6.12.y 2/2] LoongArch: vDSO: Emit GNU_EH_FRAME correctly Date: Wed, 1 Apr 2026 12:16:14 -0400 Message-ID: <20260401161614.113725-2-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260401161614.113725-1-sashal@kernel.org> References: <2026033044-kilometer-hefty-7423@gregkh> <20260401161614.113725-1-sashal@kernel.org> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Xi Ruoyao [ Upstream commit e4878c37f6679fdea91b27a0f4e60a871f0b7bad ] With -fno-asynchronous-unwind-tables and --no-eh-frame-hdr (the default of the linker), the GNU_EH_FRAME segment (specified by vdso.lds.S) is empty. This is not valid, as the current DWARF specification mandates the first byte of the EH frame to be the version number 1. It causes some unwinders to complain, for example the ClickHouse query profiler spams the log with messages: clickhouse-server[365854]: libunwind: unsupported .eh_frame_hdr version: 127 at 7ffffffb0000 Here "127" is just the byte located at the p_vaddr (0, i.e. the beginning of the vDSO) of the empty GNU_EH_FRAME segment. Cross- checking with /proc/365854/maps has also proven 7ffffffb0000 is the start of vDSO in the process VM image. In LoongArch the -fno-asynchronous-unwind-tables option seems just a MIPS legacy, and MIPS only uses this option to satisfy the MIPS-specific "genvdso" program, per the commit cfd75c2db17e ("MIPS: VDSO: Explicitly use -fno-asynchronous-unwind-tables"). IIRC it indicates some inherent limitation of the MIPS ELF ABI and has nothing to do with LoongArch. So we can simply flip it over to -fasynchronous-unwind-tables and pass --eh-frame-hdr for linking the vDSO, allowing the profilers to unwind the stack for statistics even if the sample point is taken when the PC is in the vDSO. However simply adjusting the options above would exploit an issue: when the libgcc unwinder saw the invalid GNU_EH_FRAME segment, it silently falled back to a machine-specific routine to match the code pattern of rt_sigreturn() and extract the registers saved in the sigframe if the code pattern is matched. As unwinding from signal handlers is vital for libgcc to support pthread cancellation etc., the fall-back routine had been silently keeping the LoongArch Linux systems functioning since Linux 5.19. But when we start to emit GNU_EH_FRAME with the correct format, fall-back routine will no longer be used and libgcc will fail to unwind the sigframe, and unwinding from signal handlers will no longer work, causing dozens of glibc test failures. To make it possible to unwind from signal handlers again, it's necessary to code the unwind info in __vdso_rt_sigreturn via .cfi_* directives. The offsets in the .cfi_* directives depend on the layout of struct sigframe, notably the offset of sigcontext in the sigframe. To use the offset in the assembly file, factor out struct sigframe into a header to allow asm-offsets.c to output the offset for assembly. To work around a long-term issue in the libgcc unwinder (the pc is unconditionally substracted by 1: doing so is technically incorrect for a signal frame), a nop instruction is included with the two real instructions in __vdso_rt_sigreturn in the same FDE PC range. The same hack has been used on x86 for a long time. Cc: stable@vger.kernel.org Fixes: c6b99bed6b8f ("LoongArch: Add VDSO and VSYSCALL support") Signed-off-by: Xi Ruoyao Signed-off-by: Huacai Chen Signed-off-by: Sasha Levin --- arch/loongarch/include/asm/linkage.h | 36 +++++++++++++++++++++++++++ arch/loongarch/include/asm/sigframe.h | 9 +++++++ arch/loongarch/kernel/asm-offsets.c | 2 ++ arch/loongarch/kernel/signal.c | 6 +---- arch/loongarch/vdso/Makefile | 4 +-- arch/loongarch/vdso/sigreturn.S | 6 ++--- 6 files changed, 53 insertions(+), 10 deletions(-) create mode 100644 arch/loongarch/include/asm/sigframe.h diff --git a/arch/loongarch/include/asm/linkage.h b/arch/loongarch/include/asm/linkage.h index e2eca1a25b4ef..a1bd6a3ee03a1 100644 --- a/arch/loongarch/include/asm/linkage.h +++ b/arch/loongarch/include/asm/linkage.h @@ -41,4 +41,40 @@ .cfi_endproc; \ SYM_END(name, SYM_T_NONE) +/* + * This is for the signal handler trampoline, which is used as the return + * address of the signal handlers in userspace instead of called normally. + * The long standing libgcc bug https://gcc.gnu.org/PR124050 requires a + * nop between .cfi_startproc and the actual address of the trampoline, so + * we cannot simply use SYM_FUNC_START. + * + * This wrapper also contains all the .cfi_* directives for recovering + * the content of the GPRs and the "return address" (where the rt_sigreturn + * syscall will jump to), assuming there is a struct rt_sigframe (where + * a struct sigcontext containing those information we need to recover) at + * $sp. The "DWARF for the LoongArch(TM) Architecture" manual states + * column 0 is for $zero, but it does not make too much sense to + * save/restore the hardware zero register. Repurpose this column here + * for the return address (here it's not the content of $ra we cannot use + * the default column 3). + */ +#define SYM_SIGFUNC_START(name) \ + .cfi_startproc; \ + .cfi_signal_frame; \ + .cfi_def_cfa 3, RT_SIGFRAME_SC; \ + .cfi_return_column 0; \ + .cfi_offset 0, SC_PC; \ + \ + .irp num, 1, 2, 3, 4, 5, 6, 7, 8, \ + 9, 10, 11, 12, 13, 14, 15, 16, \ + 17, 18, 19, 20, 21, 22, 23, 24, \ + 25, 26, 27, 28, 29, 30, 31; \ + .cfi_offset \num, SC_REGS + \num * SZREG; \ + .endr; \ + \ + nop; \ + SYM_START(name, SYM_L_GLOBAL, SYM_A_ALIGN) + +#define SYM_SIGFUNC_END(name) SYM_FUNC_END(name) + #endif diff --git a/arch/loongarch/include/asm/sigframe.h b/arch/loongarch/include/asm/sigframe.h new file mode 100644 index 0000000000000..109298b8d7e0b --- /dev/null +++ b/arch/loongarch/include/asm/sigframe.h @@ -0,0 +1,9 @@ +/* SPDX-License-Identifier: GPL-2.0+ */ + +#include +#include + +struct rt_sigframe { + struct siginfo rs_info; + struct ucontext rs_uctx; +}; diff --git a/arch/loongarch/kernel/asm-offsets.c b/arch/loongarch/kernel/asm-offsets.c index e476c143181a7..1ad6d9e2c4328 100644 --- a/arch/loongarch/kernel/asm-offsets.c +++ b/arch/loongarch/kernel/asm-offsets.c @@ -16,6 +16,7 @@ #include #include #include +#include #include static void __used output_ptreg_defines(void) @@ -220,6 +221,7 @@ static void __used output_sc_defines(void) COMMENT("Linux sigcontext offsets."); OFFSET(SC_REGS, sigcontext, sc_regs); OFFSET(SC_PC, sigcontext, sc_pc); + OFFSET(RT_SIGFRAME_SC, rt_sigframe, rs_uctx.uc_mcontext); BLANK(); } diff --git a/arch/loongarch/kernel/signal.c b/arch/loongarch/kernel/signal.c index c9f7ca778364e..d4151d2fb82ee 100644 --- a/arch/loongarch/kernel/signal.c +++ b/arch/loongarch/kernel/signal.c @@ -35,6 +35,7 @@ #include #include #include +#include #include #include @@ -51,11 +52,6 @@ #define lock_lbt_owner() ({ preempt_disable(); pagefault_disable(); }) #define unlock_lbt_owner() ({ pagefault_enable(); preempt_enable(); }) -struct rt_sigframe { - struct siginfo rs_info; - struct ucontext rs_uctx; -}; - struct _ctx_layout { struct sctx_info *addr; unsigned int size; diff --git a/arch/loongarch/vdso/Makefile b/arch/loongarch/vdso/Makefile index 49af37f781bbe..b37cda6346443 100644 --- a/arch/loongarch/vdso/Makefile +++ b/arch/loongarch/vdso/Makefile @@ -21,7 +21,7 @@ cflags-vdso := $(ccflags-vdso) \ $(filter -W%,$(filter-out -Wa$(comma)%,$(KBUILD_CFLAGS))) \ -std=gnu11 -O2 -g -fno-strict-aliasing -fno-common -fno-builtin \ -fno-stack-protector -fno-jump-tables -DDISABLE_BRANCH_PROFILING \ - $(call cc-option, -fno-asynchronous-unwind-tables) \ + $(call cc-option, -fasynchronous-unwind-tables) \ $(call cc-option, -fno-stack-protector) aflags-vdso := $(ccflags-vdso) \ -D__ASSEMBLY__ -Wa,-gdwarf-2 @@ -36,7 +36,7 @@ endif # VDSO linker flags. ldflags-y := -Bsymbolic --no-undefined -soname=linux-vdso.so.1 \ - $(filter -E%,$(KBUILD_CFLAGS)) -shared --build-id -T + $(filter -E%,$(KBUILD_CFLAGS)) -shared --build-id --eh-frame-hdr -T # # Shared build commands. diff --git a/arch/loongarch/vdso/sigreturn.S b/arch/loongarch/vdso/sigreturn.S index 9cb3c58fad03b..59f940d928de7 100644 --- a/arch/loongarch/vdso/sigreturn.S +++ b/arch/loongarch/vdso/sigreturn.S @@ -12,13 +12,13 @@ #include #include +#include .section .text - .cfi_sections .debug_frame -SYM_FUNC_START(__vdso_rt_sigreturn) +SYM_SIGFUNC_START(__vdso_rt_sigreturn) li.w a7, __NR_rt_sigreturn syscall 0 -SYM_FUNC_END(__vdso_rt_sigreturn) +SYM_SIGFUNC_END(__vdso_rt_sigreturn) -- 2.53.0