[PATCH v2 04/14] riscv: Adjust assembly routines to support landing pad
Jesse Huang
jesse.huang@sifive.com
Wed Jul 23 07:23:00 GMT 2025
Do you have any concern that we are going to change something as about
unlabel scheme in the future?
2025年7月23日(水) 4:28 Deepak Gupta <debug@rivosinc.com>:
> On Fri, Jul 11, 2025 at 06:52:45AM -0700, Jesse Huang wrote:
> >Landing pads, instructions for setting the label value as well as
> >alignment directives are inserted at where they should be.
> >
> >Frame offsets for floating point registers in _dl_runtime_resolve
> >are also adjusted because now t2 has to be saved onto the stack.
> >
> >Co-authored-by: Hau Hsu <hau.hsu@sifive.com>
> >Co-authored-by: Kito Cheng <kito.cheng@sifive.com>
> >---
> > sysdeps/riscv/__longjmp.S | 1 +
> > sysdeps/riscv/crti.S | 4 ++
> > sysdeps/riscv/crtn.S | 4 ++
> > sysdeps/riscv/dl-machine.h | 8 +++
> > sysdeps/riscv/dl-trampoline.S | 61 +++++++++++------
> > sysdeps/riscv/multiarch/memcpy_noalignment.S | 4 ++
> > sysdeps/riscv/setjmp.S | 3 +
> > sysdeps/riscv/start.S | 10 +++
> > sysdeps/unix/sysv/linux/riscv/clone.S | 2 +
> > sysdeps/unix/sysv/linux/riscv/sysdep.S | 1 +
> > sysdeps/unix/sysv/linux/riscv/sysdep.h | 71 ++++++++++++++++++++
> > sysdeps/unix/sysv/linux/riscv/vfork.S | 1 +
> > 12 files changed, 150 insertions(+), 20 deletions(-)
> > create mode 100644 sysdeps/riscv/crti.S
> > create mode 100644 sysdeps/riscv/crtn.S
> >
> >diff --git a/sysdeps/riscv/__longjmp.S b/sysdeps/riscv/__longjmp.S
> >index 7228b457a6..47ff3aa09e 100644
> >--- a/sysdeps/riscv/__longjmp.S
> >+++ b/sysdeps/riscv/__longjmp.S
> >@@ -20,6 +20,7 @@
> > #include <sys/asm.h>
> >
> > ENTRY (__longjmp)
> >+ LPAD
> > REG_L ra, 0*SZREG(a0)
> > REG_L s0, 1*SZREG(a0)
> > REG_L s1, 2*SZREG(a0)
> >diff --git a/sysdeps/riscv/crti.S b/sysdeps/riscv/crti.S
> >new file mode 100644
> >index 0000000000..fb1097c5ca
> >--- /dev/null
> >+++ b/sysdeps/riscv/crti.S
> >@@ -0,0 +1,4 @@
> >+/* crti.S is empty because .init_array/.fini_array are used exclusively.
> >+ Include sysdep.h to define gnu property if necessary. */
> >+
> >+#include <sysdep.h>
> >diff --git a/sysdeps/riscv/crtn.S b/sysdeps/riscv/crtn.S
> >new file mode 100644
> >index 0000000000..b2e7cb692e
> >--- /dev/null
> >+++ b/sysdeps/riscv/crtn.S
> >@@ -0,0 +1,4 @@
> >+/* crtn.S is empty because .init_array/.fini_array are used exclusively.
> >+ Include sysdep.h to define gnu property if necessary. */
> >+
> >+#include <sysdep.h>
> >diff --git a/sysdeps/riscv/dl-machine.h b/sysdeps/riscv/dl-machine.h
> >index dcc3e0883b..76f43a242b 100644
> >--- a/sysdeps/riscv/dl-machine.h
> >+++ b/sysdeps/riscv/dl-machine.h
> >@@ -28,6 +28,13 @@
> > #include <dl-irel.h>
> > #include <dl-static-tls.h>
> > #include <dl-machine-rel.h>
> >+/* This is a marker to remind us to add real expansion to setup the label
> >+ for the function signature label scheme in the future */
> >+#ifdef __riscv_landing_pad_unlabeled
> >+# define SET_LPAD
> >+#else
> >+# define SET_LPAD
> >+#endif
> >
> > #ifndef _RTLD_PROLOGUE
> > # define _RTLD_PROLOGUE(entry)
> \
> >@@ -126,6 +133,7 @@ elf_machine_dynamic (void)
> > # Pass our finalizer function to _start.\n\
> > lla a0, _dl_fini\n\
> > # Jump to the user entry point.\n\
> >+ " STRINGXV (SET_LPAD) "\n\
> > jr s0\n\
> > " _RTLD_EPILOGUE (ENTRY_POINT) \
> > _RTLD_EPILOGUE (_dl_start_user) "\
> >diff --git a/sysdeps/riscv/dl-trampoline.S b/sysdeps/riscv/dl-trampoline.S
> >index 93d04af326..2b25f64a3b 100644
> >--- a/sysdeps/riscv/dl-trampoline.S
> >+++ b/sysdeps/riscv/dl-trampoline.S
> >@@ -25,13 +25,27 @@
> > /* Assembler veneer called from the PLT header code for lazy loading.
> > The PLT header passes its own args in t0-t2. */
> >
> >-#ifdef __riscv_float_abi_soft
> >-# define FRAME_SIZE (-((-10 * SZREG) & ALMASK))
> >-#else
> >-# define FRAME_SIZE (-((-10 * SZREG - 8 * SZFREG) & ALMASK))
> >+#ifdef __riscv_landing_pad
> >+
> >+# ifdef __riscv_float_abi_soft
> >+# define FRAME_SIZE (-((-11 * SZREG) & ALMASK))
> >+# else
> >+# define FRAME_SIZE (-((-11 * SZREG - 8 * SZFREG) & ALMASK))
> >+# define FREG_BASE_OFFSET (11*SZREG)
> >+# endif
> >+
> >+# else
> >+
> >+# ifdef __riscv_float_abi_soft
> >+# define FRAME_SIZE (-((-10 * SZREG) & ALMASK))
> >+# else
> >+# define FRAME_SIZE (-((-10 * SZREG - 8 * SZFREG) & ALMASK))
> >+# define FREG_BASE_OFFSET (10*SZREG)
> >+# endif
> > #endif
> >
> > ENTRY (_dl_runtime_resolve)
> >+ LPAD
> > # Save arguments to stack.
> > addi sp, sp, -FRAME_SIZE
> > REG_S ra, 9*SZREG(sp)
> >@@ -43,16 +57,19 @@ ENTRY (_dl_runtime_resolve)
> > REG_S a5, 6*SZREG(sp)
> > REG_S a6, 7*SZREG(sp)
> > REG_S a7, 8*SZREG(sp)
> >+#ifdef __riscv_landing_pad
> >+ REG_S t2, 10*SZREG(sp)
> >+#endif
> >
> > #ifndef __riscv_float_abi_soft
> >- FREG_S fa0, (10*SZREG + 0*SZFREG)(sp)
> >- FREG_S fa1, (10*SZREG + 1*SZFREG)(sp)
> >- FREG_S fa2, (10*SZREG + 2*SZFREG)(sp)
> >- FREG_S fa3, (10*SZREG + 3*SZFREG)(sp)
> >- FREG_S fa4, (10*SZREG + 4*SZFREG)(sp)
> >- FREG_S fa5, (10*SZREG + 5*SZFREG)(sp)
> >- FREG_S fa6, (10*SZREG + 6*SZFREG)(sp)
> >- FREG_S fa7, (10*SZREG + 7*SZFREG)(sp)
> >+ FREG_S fa0, (FREG_BASE_OFFSET + 0*SZFREG)(sp)
> >+ FREG_S fa1, (FREG_BASE_OFFSET + 1*SZFREG)(sp)
> >+ FREG_S fa2, (FREG_BASE_OFFSET + 2*SZFREG)(sp)
> >+ FREG_S fa3, (FREG_BASE_OFFSET + 3*SZFREG)(sp)
> >+ FREG_S fa4, (FREG_BASE_OFFSET + 4*SZFREG)(sp)
> >+ FREG_S fa5, (FREG_BASE_OFFSET + 5*SZFREG)(sp)
> >+ FREG_S fa6, (FREG_BASE_OFFSET + 6*SZFREG)(sp)
> >+ FREG_S fa7, (FREG_BASE_OFFSET + 7*SZFREG)(sp)
> > #endif
> >
> > # Update .got.plt and obtain runtime address of callee.
> >@@ -60,6 +77,7 @@ ENTRY (_dl_runtime_resolve)
> > mv a0, t0 # link map
> > add a1, a1, t1 # reloc offset (== thrice the .got.plt offset)
> > la a2, _dl_fixup
> >+ SET_LPAD
> > jalr a2
> > mv t1, a0
> >
> >@@ -73,16 +91,19 @@ ENTRY (_dl_runtime_resolve)
> > REG_L a5, 6*SZREG(sp)
> > REG_L a6, 7*SZREG(sp)
> > REG_L a7, 8*SZREG(sp)
> >+#ifdef __riscv_landing_pad
> >+ REG_L t2, 10*SZREG(sp)
> >+#endif
> >
> > #ifndef __riscv_float_abi_soft
> >- FREG_L fa0, (10*SZREG + 0*SZFREG)(sp)
> >- FREG_L fa1, (10*SZREG + 1*SZFREG)(sp)
> >- FREG_L fa2, (10*SZREG + 2*SZFREG)(sp)
> >- FREG_L fa3, (10*SZREG + 3*SZFREG)(sp)
> >- FREG_L fa4, (10*SZREG + 4*SZFREG)(sp)
> >- FREG_L fa5, (10*SZREG + 5*SZFREG)(sp)
> >- FREG_L fa6, (10*SZREG + 6*SZFREG)(sp)
> >- FREG_L fa7, (10*SZREG + 7*SZFREG)(sp)
> >+ FREG_L fa0, (FREG_BASE_OFFSET + 0*SZFREG)(sp)
> >+ FREG_L fa1, (FREG_BASE_OFFSET + 1*SZFREG)(sp)
> >+ FREG_L fa2, (FREG_BASE_OFFSET + 2*SZFREG)(sp)
> >+ FREG_L fa3, (FREG_BASE_OFFSET + 3*SZFREG)(sp)
> >+ FREG_L fa4, (FREG_BASE_OFFSET + 4*SZFREG)(sp)
> >+ FREG_L fa5, (FREG_BASE_OFFSET + 5*SZFREG)(sp)
> >+ FREG_L fa6, (FREG_BASE_OFFSET + 6*SZFREG)(sp)
> >+ FREG_L fa7, (FREG_BASE_OFFSET + 7*SZFREG)(sp)
> > #endif
> >
> > addi sp, sp, FRAME_SIZE
> >diff --git a/sysdeps/riscv/multiarch/memcpy_noalignment.S
> b/sysdeps/riscv/multiarch/memcpy_noalignment.S
> >index dd135f4a4d..e97748e82b 100644
> >--- a/sysdeps/riscv/multiarch/memcpy_noalignment.S
> >+++ b/sysdeps/riscv/multiarch/memcpy_noalignment.S
> >@@ -34,7 +34,11 @@
> > #define BLOCK_SIZE (16 * SZREG)
> >
> > .attribute unaligned_access, 1
> >+#ifdef __riscv_landing_pad
> >+ .align 2
> >+#endif
> > ENTRY (__memcpy_noalignment)
> >+ LPAD
> > beq a2, zero, L(ret)
> >
> > /* if LEN < SZREG jump to tail handling. */
> >diff --git a/sysdeps/riscv/setjmp.S b/sysdeps/riscv/setjmp.S
> >index 600ea84db6..df048cb544 100644
> >--- a/sysdeps/riscv/setjmp.S
> >+++ b/sysdeps/riscv/setjmp.S
> >@@ -20,14 +20,17 @@
> > #include <sys/asm.h>
> >
> > ENTRY (_setjmp)
> >+ LPAD
> > li a1, 0
> > j HIDDEN_JUMPTARGET (__sigsetjmp)
> > END (_setjmp)
> > ENTRY (setjmp)
> >+ LPAD
> > li a1, 1
> > /* Fallthrough */
> > END (setjmp)
> > ENTRY (__sigsetjmp)
> >+ LPAD
> > REG_S ra, 0*SZREG(a0)
> > REG_S s0, 1*SZREG(a0)
> > REG_S s1, 2*SZREG(a0)
> >diff --git a/sysdeps/riscv/start.S b/sysdeps/riscv/start.S
> >index 2db79c0ae6..ff083b13a4 100644
> >--- a/sysdeps/riscv/start.S
> >+++ b/sysdeps/riscv/start.S
> >@@ -47,12 +47,14 @@ ENTRY (ENTRY_POINT)
> > .cfi_label to force starting the FDE. */
> > .cfi_label .Ldummy
> > cfi_undefined (ra)
> >+ LPAD
> > call load_gp
> > mv a5, a0 /* rtld_fini. */
> > /* main may be in a shared library. */
> > #if defined PIC && !defined SHARED
> > /* Avoid relocation in static PIE since _start is called before it
> > is relocated. */
> >+ SET_LPAD
> > lla a0, __wrap_main
> > #else
> > la a0, main
> >@@ -69,7 +71,11 @@ ENTRY (ENTRY_POINT)
> > END (ENTRY_POINT)
> >
> > #if defined PIC && !defined SHARED
> >+#ifdef __riscv_landing_pad
> >+ .align 2
> >+#endif /* __riscv_landing_pad */
> > __wrap_main:
> >+ LPAD
> > tail main@plt
> > #endif
> >
> >@@ -79,9 +85,13 @@ __wrap_main:
> > needs to be initialized before calling __libc_start_main in that case.
> > So we redundantly initialize it at the beginning of _start. */
> >
> >+#ifdef __riscv_landing_pad
> >+ .align 2
> >+#endif /* __riscv_landing_pad */
> > load_gp:
> > .option push
> > .option norelax
> >+ LPAD
> > lla gp, __global_pointer$
> > .option pop
> > ret
> >diff --git a/sysdeps/unix/sysv/linux/riscv/clone.S
> b/sysdeps/unix/sysv/linux/riscv/clone.S
> >index 1362dd9c22..d6a0996ec8 100644
> >--- a/sysdeps/unix/sysv/linux/riscv/clone.S
> >+++ b/sysdeps/unix/sysv/linux/riscv/clone.S
> >@@ -31,6 +31,7 @@
> >
> > .text
> > LEAF (__clone)
> >+ LPAD
> >
> > /* Align stack to a 128-bit boundary as per RISC-V ABI. */
> > andi a1,a1,ALMASK
> >@@ -82,6 +83,7 @@ L (thread_start):
> > REG_L a0,SZREG(sp) /* Argument pointer. */
> >
> > /* Call the user's function. */
> >+ SET_LPAD
> > jalr a1
> >
> > /* Call exit with the function's return value. */
> >diff --git a/sysdeps/unix/sysv/linux/riscv/sysdep.S
> b/sysdeps/unix/sysv/linux/riscv/sysdep.S
> >index b50671b9b7..e7ea424e45 100644
> >--- a/sysdeps/unix/sysv/linux/riscv/sysdep.S
> >+++ b/sysdeps/unix/sysv/linux/riscv/sysdep.S
> >@@ -23,6 +23,7 @@
> > #endif
> >
> > ENTRY (__syscall_error)
> >+ LPAD
> > mv t0, ra
> > /* Fall through to __syscall_set_errno. */
> > END (__syscall_error)
> >diff --git a/sysdeps/unix/sysv/linux/riscv/sysdep.h
> b/sysdeps/unix/sysv/linux/riscv/sysdep.h
> >index ee015dfeb6..14a1f3a647 100644
> >--- a/sysdeps/unix/sysv/linux/riscv/sysdep.h
> >+++ b/sysdeps/unix/sysv/linux/riscv/sysdep.h
> >@@ -53,6 +53,75 @@
> >
> > # include <sys/asm.h>
> >
> >+/* GNU_PROPERTY_RISCV_* macros from elf.h for use in asm code. */
> >+#define FEATURE_1_AND 0xc0000000
> >+
> >+/* Add a NT_GNU_PROPERTY_TYPE_0 note. */
> >+#if __riscv_xlen == 32
> >+# define GNU_PROPERTY(type, value) \
> >+ .section .note.gnu.property, "a"; \
> >+ .p2align 2; \
> >+ .word 4; \
> >+ .word 12; \
> >+ .word 5; \
> >+ .asciz "GNU"; \
> >+ .word type; \
> >+ .word 4; \
> >+ .word value; \
> >+ .text
> >+#else
> >+# define GNU_PROPERTY(type, value) \
> >+ .section .note.gnu.property, "a"; \
> >+ .p2align 3; \
> >+ .word 4; \
> >+ .word 16; \
> >+ .word 5; \
> >+ .asciz "GNU"; \
> >+ .word type; \
> >+ .word 4; \
> >+ .word value; \
> >+ .word 0; \
> >+ .text
> >+#endif
>
> + Heinrich
>
> Do we need a version field for unlabeled landing pad scheme?
> I have raised it with Kito, for labeled one's we need version for sure.
> Although if we start with unlabaled gnu property, it will look
> canonical.
>
> >+
> >+/* Add GNU property note with the supported features to all asm code
> >+ where sysdep.h is included. */
> >+#undef __VALUE_FOR_FEATURE_1_AND
> >+#if defined (__riscv_landing_pad) || defined (__riscv_shadow_stack)
> >+# if defined (__riscv_landing_pad_unlabeled)
> >+# if defined (__riscv_shadow_stack)
> >+# define __VALUE_FOR_FEATURE_1_AND 0x3
> >+# else
> >+# define __VALUE_FOR_FEATURE_1_AND 0x1
> >+# endif
> >+# elif defined (__riscv_landing_pad_func_sig)
> >+# if defined (__riscv_shadow_stack)
> >+# define __VALUE_FOR_FEATURE_1_AND 0x6
> >+# else
> >+# define __VALUE_FOR_FEATURE_1_AND 0x4
> >+# endif
> >+# else
> >+# if defined (__riscv_shadow_stack)
> >+# define __VALUE_FOR_FEATURE_1_AND 0x2
> >+# else
> >+# error "What?"
> >+# endif
> >+# endif
> >+#endif
> >+
> >+#if defined (__VALUE_FOR_FEATURE_1_AND)
> >+GNU_PROPERTY (FEATURE_1_AND, __VALUE_FOR_FEATURE_1_AND)
> >+#endif
> >+#undef __VALUE_FOR_FEATURE_1_AND
> >+
> >+#ifdef __riscv_landing_pad_unlabeled
> >+# define SET_LPAD
> >+# define LPAD lpad 0
> >+#else
> >+# define SET_LPAD
> >+# define LPAD
> >+#endif
> >+
> > # define ENTRY(name) LEAF(name)
> >
> > # define L(label) .L ## label
> >@@ -64,6 +133,7 @@
> > .text; \
> > .align 2; \
> > ENTRY (name); \
> >+ LPAD; \
> > li a7, SYS_ify (syscall_name); \
> > scall; \
> > li a7, -4096; \
> >@@ -111,6 +181,7 @@
> > # define PSEUDO_NOERRNO(name, syscall_name, args) \
> > .align 2; \
> > ENTRY (name); \
> >+ LPAD; \
> > li a7, SYS_ify (syscall_name); \
> > scall;
> >
> >diff --git a/sysdeps/unix/sysv/linux/riscv/vfork.S
> b/sysdeps/unix/sysv/linux/riscv/vfork.S
> >index 1e39b7a057..4cf7b5a9d8 100644
> >--- a/sysdeps/unix/sysv/linux/riscv/vfork.S
> >+++ b/sysdeps/unix/sysv/linux/riscv/vfork.S
> >@@ -29,6 +29,7 @@
> >
> > .text
> > LEAF (__libc_vfork)
> >+ LPAD
> >
> > li a0, (CLONE_VFORK | CLONE_VM | SIGCHLD)
> > mv a1, sp
> >--
> >2.39.3
> >
>
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