RISC-V: Allow long jumps to __syscall_error
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Commit Message
__syscall_error may end up farther than 1MiB away from a caller,
especially when linking statically large binaries. la+jr allow for
4GiB jumps.
Fixes: 36960f0c76 ("RISC-V: Linux Syscall Interface")
Fixes: 7f33b09c65 ("RISC-V: Linux ABI")
Signed-off-by: Łukasz Stelmach <l.stelmach@samsung.com>
---
I was compiling and statically linking GNU Guile and I was getting a
lot of messages like this:
/usr/lib64/libc.a(uname.o): in function `__uname':
(.text+0x10): relocation truncated to fit: R_RISCV_JAL against symbol `__syscall_error' defined in .text section in /usr/lib64/libc.a(sysdep.o)
And indeed in uname.o there was a relative jump which was marked as
R_RISCV_JAL and pointed to __syscall_error. After sucessfully linking
the binary with this fix applied __uname and __syscall_error end up
1125000 bytes apart.
--8<---------------cut here---------------end--------------->8---
Relocation section '.rela.text' at offset 0x250 contains 4 entries:
Offset Info Type Sym. Value Sym. Name + Addend
000000000000 00000000002b R_RISCV_ALIGN 2
000000000002 00000000002b R_RISCV_ALIGN 2
00000000000e 000a00000010 R_RISCV_BRANCH 0000000000000014 .Lsyscall_error__uname + 0
000000000014 000c00000011 R_RISCV_JAL 0000000000000000 __syscall_error + 0
--8<---------------cut here---------------end--------------->8---
--8<---------------cut here---------------end--------------->8---
uname.o: file format elf64-littleriscv
Disassembly of section .text:
0000000000000000 <$x>:
0: 0001 nop
2: 0001 nop
0000000000000004 <__uname>:
4: 0a000893 li a7,160
8: 00000073 ecall
c: 78fd lui a7,0xfffff
e: 00a8e363 bltu a7,a0,14 <.Lsyscall_error__uname>
12: 8082 ret
0000000000000014 <.Lsyscall_error__uname>:
14: fedff06f j 0 <$x>
^^^^ ^^^^^^^^^^^^^^
18: 8082 ret
...
--8<---------------cut here---------------end--------------->8---
I suspect the two nops that the jump points to were meant(?)/could(??) be
used (if there were more of them) to be a placeholder for a longer
jump. Alas binutils 2.38 can't handle it properly (yet?), so a manual
intervention here seems reasonable.
I have neither seen any errors regarding code in *context.S and vfork.S
files nor tested if the altered code works, but I assume it needs to be
fixed as well.
sysdeps/unix/sysv/linux/riscv/clone.S | 3 ++-
sysdeps/unix/sysv/linux/riscv/getcontext.S | 3 ++-
sysdeps/unix/sysv/linux/riscv/setcontext.S | 3 ++-
sysdeps/unix/sysv/linux/riscv/swapcontext.S | 3 ++-
sysdeps/unix/sysv/linux/riscv/sysdep.h | 3 ++-
sysdeps/unix/sysv/linux/riscv/vfork.S | 3 ++-
6 files changed, 12 insertions(+), 6 deletions(-)
Comments
Use the `tail` pseudoinstruction rather than `la` + `jr`, as this will
relax to `j` when within range.
On Fri, Sep 16, 2022 at 6:31 AM Łukasz Stelmach via Libc-alpha
<libc-alpha@sourceware.org> wrote:
>
> __syscall_error may end up farther than 1MiB away from a caller,
> especially when linking statically large binaries. la+jr allow for
> 4GiB jumps.
>
> Fixes: 36960f0c76 ("RISC-V: Linux Syscall Interface")
> Fixes: 7f33b09c65 ("RISC-V: Linux ABI")
> Signed-off-by: Łukasz Stelmach <l.stelmach@samsung.com>
> ---
>
> I was compiling and statically linking GNU Guile and I was getting a
> lot of messages like this:
>
> /usr/lib64/libc.a(uname.o): in function `__uname':
> (.text+0x10): relocation truncated to fit: R_RISCV_JAL against symbol `__syscall_error' defined in .text section in /usr/lib64/libc.a(sysdep.o)
>
> And indeed in uname.o there was a relative jump which was marked as
> R_RISCV_JAL and pointed to __syscall_error. After sucessfully linking
> the binary with this fix applied __uname and __syscall_error end up
> 1125000 bytes apart.
>
> --8<---------------cut here---------------end--------------->8---
> Relocation section '.rela.text' at offset 0x250 contains 4 entries:
> Offset Info Type Sym. Value Sym. Name + Addend
> 000000000000 00000000002b R_RISCV_ALIGN 2
> 000000000002 00000000002b R_RISCV_ALIGN 2
> 00000000000e 000a00000010 R_RISCV_BRANCH 0000000000000014 .Lsyscall_error__uname + 0
> 000000000014 000c00000011 R_RISCV_JAL 0000000000000000 __syscall_error + 0
> --8<---------------cut here---------------end--------------->8---
>
> --8<---------------cut here---------------end--------------->8---
> uname.o: file format elf64-littleriscv
>
>
> Disassembly of section .text:
>
> 0000000000000000 <$x>:
> 0: 0001 nop
> 2: 0001 nop
>
> 0000000000000004 <__uname>:
> 4: 0a000893 li a7,160
> 8: 00000073 ecall
> c: 78fd lui a7,0xfffff
> e: 00a8e363 bltu a7,a0,14 <.Lsyscall_error__uname>
> 12: 8082 ret
>
> 0000000000000014 <.Lsyscall_error__uname>:
> 14: fedff06f j 0 <$x>
> ^^^^ ^^^^^^^^^^^^^^
> 18: 8082 ret
> ...
> --8<---------------cut here---------------end--------------->8---
>
> I suspect the two nops that the jump points to were meant(?)/could(??) be
> used (if there were more of them) to be a placeholder for a longer
> jump. Alas binutils 2.38 can't handle it properly (yet?), so a manual
> intervention here seems reasonable.
>
> I have neither seen any errors regarding code in *context.S and vfork.S
> files nor tested if the altered code works, but I assume it needs to be
> fixed as well.
>
> sysdeps/unix/sysv/linux/riscv/clone.S | 3 ++-
> sysdeps/unix/sysv/linux/riscv/getcontext.S | 3 ++-
> sysdeps/unix/sysv/linux/riscv/setcontext.S | 3 ++-
> sysdeps/unix/sysv/linux/riscv/swapcontext.S | 3 ++-
> sysdeps/unix/sysv/linux/riscv/sysdep.h | 3 ++-
> sysdeps/unix/sysv/linux/riscv/vfork.S | 3 ++-
> 6 files changed, 12 insertions(+), 6 deletions(-)
>
> diff --git a/sysdeps/unix/sysv/linux/riscv/clone.S b/sysdeps/unix/sysv/linux/riscv/clone.S
> index d7d2915e87..e716285afa 100644
> --- a/sysdeps/unix/sysv/linux/riscv/clone.S
> +++ b/sysdeps/unix/sysv/linux/riscv/clone.S
> @@ -63,7 +63,8 @@ L (invalid):
> li a0, -EINVAL
> /* Something bad happened -- no child created. */
> L (error):
> - j __syscall_error
> + la t0, __syscall_error
> + jr t0
> END (__clone)
>
> /* Load up the arguments to the function. Put this block of code in
> diff --git a/sysdeps/unix/sysv/linux/riscv/getcontext.S b/sysdeps/unix/sysv/linux/riscv/getcontext.S
> index 499f70b65d..a4751ae595 100644
> --- a/sysdeps/unix/sysv/linux/riscv/getcontext.S
> +++ b/sysdeps/unix/sysv/linux/riscv/getcontext.S
> @@ -70,7 +70,8 @@ LEAF (__getcontext)
>
> ret
>
> -99: j __syscall_error
> +99: la t0, __syscall_error
> + jr t0
>
> PSEUDO_END (__getcontext)
>
> diff --git a/sysdeps/unix/sysv/linux/riscv/setcontext.S b/sysdeps/unix/sysv/linux/riscv/setcontext.S
> index e3bc84a2e6..fddd9d843f 100644
> --- a/sysdeps/unix/sysv/linux/riscv/setcontext.S
> +++ b/sysdeps/unix/sysv/linux/riscv/setcontext.S
> @@ -92,7 +92,8 @@ LEAF (__setcontext)
>
> jr t1
>
> -99: j __syscall_error
> +99: la t0, __syscall_error
> + jr t0
>
> END (__setcontext)
> libc_hidden_def (__setcontext)
> diff --git a/sysdeps/unix/sysv/linux/riscv/swapcontext.S b/sysdeps/unix/sysv/linux/riscv/swapcontext.S
> index 4da615f6d4..8e29d96595 100644
> --- a/sysdeps/unix/sysv/linux/riscv/swapcontext.S
> +++ b/sysdeps/unix/sysv/linux/riscv/swapcontext.S
> @@ -118,7 +118,8 @@ LEAF (__swapcontext)
> jr t1
>
>
> -99: j __syscall_error
> +99: la t0, __syscall_error
> + jr t0
>
> PSEUDO_END (__swapcontext)
>
> diff --git a/sysdeps/unix/sysv/linux/riscv/sysdep.h b/sysdeps/unix/sysv/linux/riscv/sysdep.h
> index 37ff07a0d7..0cd78daf2b 100644
> --- a/sysdeps/unix/sysv/linux/riscv/sysdep.h
> +++ b/sysdeps/unix/sysv/linux/riscv/sysdep.h
> @@ -102,7 +102,8 @@
> # else
> # define SYSCALL_ERROR_HANDLER(name) \
> .Lsyscall_error ## name: \
> - j __syscall_error;
> + la t0, __syscall_error; \
> + jr t0;
> # endif
>
> /* Performs a system call, not setting errno. */
> diff --git a/sysdeps/unix/sysv/linux/riscv/vfork.S b/sysdeps/unix/sysv/linux/riscv/vfork.S
> index 0970543619..8f1b2c9b3a 100644
> --- a/sysdeps/unix/sysv/linux/riscv/vfork.S
> +++ b/sysdeps/unix/sysv/linux/riscv/vfork.S
> @@ -39,7 +39,8 @@ LEAF (__libc_vfork)
> bltz a0, 1f
> ret
>
> -1: j __syscall_error
> +1: la t0, __syscall_error
> + jr t0
> END (__libc_vfork)
>
> weak_alias (__libc_vfork, vfork)
> --
> 2.30.2
>
@@ -63,7 +63,8 @@ L (invalid):
li a0, -EINVAL
/* Something bad happened -- no child created. */
L (error):
- j __syscall_error
+ la t0, __syscall_error
+ jr t0
END (__clone)
/* Load up the arguments to the function. Put this block of code in
@@ -70,7 +70,8 @@ LEAF (__getcontext)
ret
-99: j __syscall_error
+99: la t0, __syscall_error
+ jr t0
PSEUDO_END (__getcontext)
@@ -92,7 +92,8 @@ LEAF (__setcontext)
jr t1
-99: j __syscall_error
+99: la t0, __syscall_error
+ jr t0
END (__setcontext)
libc_hidden_def (__setcontext)
@@ -118,7 +118,8 @@ LEAF (__swapcontext)
jr t1
-99: j __syscall_error
+99: la t0, __syscall_error
+ jr t0
PSEUDO_END (__swapcontext)
@@ -102,7 +102,8 @@
# else
# define SYSCALL_ERROR_HANDLER(name) \
.Lsyscall_error ## name: \
- j __syscall_error;
+ la t0, __syscall_error; \
+ jr t0;
# endif
/* Performs a system call, not setting errno. */
@@ -39,7 +39,8 @@ LEAF (__libc_vfork)
bltz a0, 1f
ret
-1: j __syscall_error
+1: la t0, __syscall_error
+ jr t0
END (__libc_vfork)
weak_alias (__libc_vfork, vfork)