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 cfd75c2db1 ("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: c6b99bed6b ("LoongArch: Add VDSO and VSYSCALL support")
Signed-off-by: Xi Ruoyao <xry111@xry111.site>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
Now if preemption happens between protected_save_fpu_context() and
protected_save_lbt_context(), FTOP context is lost. Because FTOP is
saved by protected_save_lbt_context() but protected_save_fpu_context()
disables TM before that. So save LBT before FPU in setup_sigcontext()
to avoid this potential risk.
Signed-off-by: Hanlu Li <lihanlu@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
Like the other relevant symbols, export some fp, lsx, lasx and lbt
assembly symbols and put the function declarations in header files
rather than source files.
While at it, use "asmlinkage" for the other existing C prototypes
of assembly functions and also do not use the "extern" keyword with
function declarations according to the document coding-style.rst.
Cc: stable@vger.kernel.org # 6.6+
Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
loongarch's signal.c uses rseq_signal_deliver() so it should
pull in the appropriate header to prevent a build error:
../arch/loongarch/kernel/signal.c: In function 'handle_signal':
../arch/loongarch/kernel/signal.c:1034:9: error: implicit declaration of function 'rseq_signal_deliver' [-Werror=implicit-function-declaration]
1034 | rseq_signal_deliver(ksig, regs);
| ^~~~~~~~~~~~~~~~~~~
Fixes: b74baf4ad0 ("LoongArch: Add signal handling support")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Huacai Chen <chenhuacai@kernel.org>
Cc: WANG Xuerui <kernel@xen0n.name>
Cc: loongarch@lists.linux.dev
Cc: Kent Overstreet <kent.overstreet@linux.dev>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
Loongson Binary Translation (LBT) is used to accelerate binary translation,
which contains 4 scratch registers (scr0 to scr3), x86/ARM eflags (eflags)
and x87 fpu stack pointer (ftop).
This patch support kernel to save/restore these registers, handle the LBT
exception and maintain sigcontext.
Signed-off-by: Qi Hu <huqi@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
Commit 8ba62d3794 ("task_work: Call tracehook_notify_signal from
get_signal on all architectures") adjust arch_do_signal_or_restart() for
all architectures. LoongArch hasn't been upstream yet at that time and
can be still built successfully without adjustment because this function
has a weak version with the correct prototype. It is obviously that we
should convert LoongArch to use new API, otherwise some signal handlings
will be lost.
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
Add ucontext/sigcontext definition and signal handling support for
LoongArch.
Cc: Eric Biederman <ebiederm@xmission.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Reviewed-by: WANG Xuerui <git@xen0n.name>
Reviewed-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
