[libunwind] Unwind through Linux riscv sigreturn trampoline
Similar to D90898 (Linux AArch64) and D124765 (SystemZ).
On an Arch Linux RISC-V (riscv64gc), the following code
```
#define _GNU_SOURCE
#include <dlfcn.h>
#include <libunwind.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
static void handler(int signo) {
unw_context_t context;
unw_cursor_t cursor;
unw_getcontext(&context);
unw_init_local(&cursor, &context);
unw_word_t pc, sp;
do {
unw_get_reg(&cursor, UNW_REG_IP, &pc);
unw_get_reg(&cursor, UNW_REG_SP, &sp);
printf("pc=0x%016zx sp=0x%016zx", (size_t)pc, (size_t)sp);
Dl_info info = {};
if (dladdr((void *)pc, &info))
printf(" %s:%s", info.dli_fname, info.dli_sname ? info.dli_sname : "");
puts("");
} while (unw_step(&cursor) > 0);
exit(0);
}
int main() {
signal(SIGUSR1, handler);
raise(SIGUSR1);
return 1;
}
```
linked with `-Wl,--export-dynamic` gives an output like
```
pc=0x0000000000010a82 sp=0x00007fffd8a0b910 ./b:
pc=0x00007fffa7e77800 sp=0x00007fffd8a0c520 linux-vdso.so.1:__vdso_rt_sigreturn
pc=0x00007fffa7d73bee sp=0x00007fffd8a0c960 /usr/lib/libc.so.6:
pc=0x00007fffa7d3ed66 sp=0x00007fffd8a0c9b0 /usr/lib/libc.so.6:gsignal
pc=0x0000000000010a3c sp=0x00007fffd8a0c9c0 ./b:main
pc=0x00007fffa7d2f1d4 sp=0x00007fffd8a0c9e0 /usr/lib/libc.so.6:
pc=0x00007fffa7d2f27c sp=0x00007fffd8a0cb10 /usr/lib/libc.so.6:__libc_start_main
pc=0x00000000000109a0 sp=0x00007fffd8a0cb60 ./b:_start
```
Co-Authored-By: Fangrui Song <i@maskray.me>
Reviewed By: #libunwind, MaskRay
Differential Revision: https://reviews.llvm.org/D148499
GitOrigin-RevId: f56ea14c299490671c1c157a6fb08ce3e452be2d
diff --git a/src/UnwindCursor.hpp b/src/UnwindCursor.hpp
index db6d0ec..dde9477 100644
--- a/src/UnwindCursor.hpp
+++ b/src/UnwindCursor.hpp
@@ -31,7 +31,8 @@
#endif
#if defined(_LIBUNWIND_TARGET_LINUX) && \
- (defined(_LIBUNWIND_TARGET_AARCH64) || defined(_LIBUNWIND_TARGET_S390X))
+ (defined(_LIBUNWIND_TARGET_AARCH64) || defined(_LIBUNWIND_TARGET_RISCV) || \
+ defined(_LIBUNWIND_TARGET_S390X))
#include <sys/syscall.h>
#include <sys/uio.h>
#include <unistd.h>
@@ -993,6 +994,10 @@
bool setInfoForSigReturn(Registers_arm64 &);
int stepThroughSigReturn(Registers_arm64 &);
#endif
+#if defined(_LIBUNWIND_TARGET_RISCV)
+ bool setInfoForSigReturn(Registers_riscv &);
+ int stepThroughSigReturn(Registers_riscv &);
+#endif
#if defined(_LIBUNWIND_TARGET_S390X)
bool setInfoForSigReturn(Registers_s390x &);
int stepThroughSigReturn(Registers_s390x &);
@@ -2721,6 +2726,60 @@
// defined(_LIBUNWIND_TARGET_AARCH64)
#if defined(_LIBUNWIND_CHECK_LINUX_SIGRETURN) && \
+ defined(_LIBUNWIND_TARGET_RISCV)
+template <typename A, typename R>
+bool UnwindCursor<A, R>::setInfoForSigReturn(Registers_riscv &) {
+ const pint_t pc = static_cast<pint_t>(getReg(UNW_REG_IP));
+ uint32_t instructions[2];
+ struct iovec local_iov = {&instructions, sizeof instructions};
+ struct iovec remote_iov = {reinterpret_cast<void *>(pc), sizeof instructions};
+ long bytesRead =
+ syscall(SYS_process_vm_readv, getpid(), &local_iov, 1, &remote_iov, 1, 0);
+ // Look for the two instructions used in the sigreturn trampoline
+ // __vdso_rt_sigreturn:
+ //
+ // 0x08b00893 li a7,0x8b
+ // 0x00000073 ecall
+ if (bytesRead != sizeof instructions || instructions[0] != 0x08b00893 ||
+ instructions[1] != 0x00000073)
+ return false;
+
+ _info = {};
+ _info.start_ip = pc;
+ _info.end_ip = pc + 4;
+ _isSigReturn = true;
+ return true;
+}
+
+template <typename A, typename R>
+int UnwindCursor<A, R>::stepThroughSigReturn(Registers_riscv &) {
+ // In the signal trampoline frame, sp points to an rt_sigframe[1], which is:
+ // - 128-byte siginfo struct
+ // - ucontext_t struct:
+ // - 8-byte long (__uc_flags)
+ // - 8-byte pointer (*uc_link)
+ // - 24-byte uc_stack
+ // - 8-byte uc_sigmask
+ // - 120-byte of padding to allow sigset_t to be expanded in the future
+ // - 8 bytes of padding because sigcontext has 16-byte alignment
+ // - struct sigcontext uc_mcontext
+ // [1]
+ // https://github.com/torvalds/linux/blob/master/arch/riscv/kernel/signal.c
+ const pint_t kOffsetSpToSigcontext = 128 + 8 + 8 + 24 + 8 + 128;
+
+ const pint_t sigctx = _registers.getSP() + kOffsetSpToSigcontext;
+ _registers.setIP(_addressSpace.get64(sigctx));
+ for (int i = UNW_RISCV_X1; i <= UNW_RISCV_X31; ++i) {
+ uint64_t value = _addressSpace.get64(sigctx + static_cast<pint_t>(i * 8));
+ _registers.setRegister(i, value);
+ }
+ _isSignalFrame = true;
+ return UNW_STEP_SUCCESS;
+}
+#endif // defined(_LIBUNWIND_CHECK_LINUX_SIGRETURN) &&
+ // defined(_LIBUNWIND_TARGET_RISCV)
+
+#if defined(_LIBUNWIND_CHECK_LINUX_SIGRETURN) && \
defined(_LIBUNWIND_TARGET_S390X)
template <typename A, typename R>
bool UnwindCursor<A, R>::setInfoForSigReturn(Registers_s390x &) {
diff --git a/test/signal_unwind.pass.cpp b/test/signal_unwind.pass.cpp
index 2a73141..954a5d4 100644
--- a/test/signal_unwind.pass.cpp
+++ b/test/signal_unwind.pass.cpp
@@ -8,7 +8,7 @@
//===----------------------------------------------------------------------===//
// Ensure that the unwinder can cope with the signal handler.
-// REQUIRES: target={{(aarch64|s390x|x86_64)-.+linux.*}}
+// REQUIRES: target={{(aarch64|riscv64|s390x|x86_64)-.+linux.*}}
// TODO: Figure out why this fails with Memory Sanitizer.
// XFAIL: msan
diff --git a/test/unwind_leaffunction.pass.cpp b/test/unwind_leaffunction.pass.cpp
index c1b223b..8c9912e 100644
--- a/test/unwind_leaffunction.pass.cpp
+++ b/test/unwind_leaffunction.pass.cpp
@@ -8,7 +8,7 @@
//===----------------------------------------------------------------------===//
// Ensure that leaf function can be unwund.
-// REQUIRES: target={{(aarch64|s390x|x86_64)-.+linux.*}}
+// REQUIRES: target={{(aarch64|riscv64|s390x|x86_64)-.+linux.*}}
// TODO: Figure out why this fails with Memory Sanitizer.
// XFAIL: msan
