RISC-V: jal cannot refer to a default visibility symbol for shared object.

This is the original binutils bugzilla report,
https://sourceware.org/bugzilla/show_bug.cgi?id=28509

And this is the first version of the proposed binutils patch,
https://sourceware.org/pipermail/binutils/2021-November/118398.html

After applying the binutils patch, I get the the unexpected error when
building libgcc,

/scratch/nelsonc/riscv-gnu-toolchain/riscv-gcc/libgcc/config/riscv/div.S:42:
/scratch/nelsonc/build-upstream/rv64gc-linux/build-install/riscv64-unknown-linux-gnu/bin/ld: relocation R_RISCV_JAL against `__udivdi3' which may bind externally can not be used when making a shared object; recompile with -fPIC

Therefore, this patch add an extra hidden alias symbol for __udivdi3, and
then use HIDDEN_JUMPTARGET to target a non-preemptible symbol instead.
The solution is similar to glibc as follows,
https://sourceware.org/git/?p=glibc.git;a=commit;h=68389203832ab39dd0dbaabbc4059e7fff51c29b

libgcc/ChangeLog:

	* config/riscv/div.S: Add the hidden alias symbol for __udivdi3, and
	then use HIDDEN_JUMPTARGET to target it since it is non-preemptible.
	* config/riscv/riscv-asm.h: Added new macros HIDDEN_JUMPTARGET and
	HIDDEN_DEF.
---
 libgcc/config/riscv/div.S       | 15 ++++++++-------
 libgcc/config/riscv/riscv-asm.h |  6 ++++++
 2 files changed, 14 insertions(+), 7 deletions(-)

Committed, thanks :)

On Mon, Nov 29, 2021 at 8:48 PM Nelson Chu <nelson.chu@sifive.com> wrote:
>
> This is the original binutils bugzilla report,
> https://sourceware.org/bugzilla/show_bug.cgi?id=28509
>
> And this is the first version of the proposed binutils patch,
> https://sourceware.org/pipermail/binutils/2021-November/118398.html
>
> After applying the binutils patch, I get the the unexpected error when
> building libgcc,
>
> /scratch/nelsonc/riscv-gnu-toolchain/riscv-gcc/libgcc/config/riscv/div.S:42:
> /scratch/nelsonc/build-upstream/rv64gc-linux/build-install/riscv64-unknown-linux-gnu/bin/ld: relocation R_RISCV_JAL against `__udivdi3' which may bind externally can not be used when making a shared object; recompile with -fPIC
>
> Therefore, this patch add an extra hidden alias symbol for __udivdi3, and
> then use HIDDEN_JUMPTARGET to target a non-preemptible symbol instead.
> The solution is similar to glibc as follows,
> https://sourceware.org/git/?p=glibc.git;a=commit;h=68389203832ab39dd0dbaabbc4059e7fff51c29b
>
> libgcc/ChangeLog:
>
>         * config/riscv/div.S: Add the hidden alias symbol for __udivdi3, and
>         then use HIDDEN_JUMPTARGET to target it since it is non-preemptible.
>         * config/riscv/riscv-asm.h: Added new macros HIDDEN_JUMPTARGET and
>         HIDDEN_DEF.
> ---
>  libgcc/config/riscv/div.S       | 15 ++++++++-------
>  libgcc/config/riscv/riscv-asm.h |  6 ++++++
>  2 files changed, 14 insertions(+), 7 deletions(-)
>
> diff --git a/libgcc/config/riscv/div.S b/libgcc/config/riscv/div.S
> index c9bd787..723c3b8 100644
> --- a/libgcc/config/riscv/div.S
> +++ b/libgcc/config/riscv/div.S
> @@ -40,7 +40,7 @@ FUNC_BEGIN (__udivsi3)
>    sll    a0, a0, 32
>    sll    a1, a1, 32
>    move   t0, ra
> -  jal    __udivdi3
> +  jal    HIDDEN_JUMPTARGET(__udivdi3)
>    sext.w a0, a0
>    jr     t0
>  FUNC_END (__udivsi3)
> @@ -52,7 +52,7 @@ FUNC_BEGIN (__umodsi3)
>    srl    a0, a0, 32
>    srl    a1, a1, 32
>    move   t0, ra
> -  jal    __udivdi3
> +  jal    HIDDEN_JUMPTARGET(__udivdi3)
>    sext.w a0, a1
>    jr     t0
>  FUNC_END (__umodsi3)
> @@ -95,11 +95,12 @@ FUNC_BEGIN (__udivdi3)
>  .L5:
>    ret
>  FUNC_END (__udivdi3)
> +HIDDEN_DEF (__udivdi3)
>
>  FUNC_BEGIN (__umoddi3)
>    /* Call __udivdi3(a0, a1), then return the remainder, which is in a1.  */
>    move  t0, ra
> -  jal   __udivdi3
> +  jal   HIDDEN_JUMPTARGET(__udivdi3)
>    move  a0, a1
>    jr    t0
>  FUNC_END (__umoddi3)
> @@ -111,12 +112,12 @@ FUNC_END (__umoddi3)
>    bgtz  a1, .L12     /* Compute __udivdi3(-a0, a1), then negate the result.  */
>
>    neg   a1, a1
> -  j     __udivdi3    /* Compute __udivdi3(-a0, -a1).  */
> +  j     HIDDEN_JUMPTARGET(__udivdi3)     /* Compute __udivdi3(-a0, -a1).  */
>  .L11:                /* Compute __udivdi3(a0, -a1), then negate the result.  */
>    neg   a1, a1
>  .L12:
>    move  t0, ra
> -  jal   __udivdi3
> +  jal   HIDDEN_JUMPTARGET(__udivdi3)
>    neg   a0, a0
>    jr    t0
>  FUNC_END (__divdi3)
> @@ -126,7 +127,7 @@ FUNC_BEGIN (__moddi3)
>    bltz   a1, .L31
>    bltz   a0, .L32
>  .L30:
> -  jal    __udivdi3    /* The dividend is not negative.  */
> +  jal    HIDDEN_JUMPTARGET(__udivdi3)    /* The dividend is not negative.  */
>    move   a0, a1
>    jr     t0
>  .L31:
> @@ -134,7 +135,7 @@ FUNC_BEGIN (__moddi3)
>    bgez   a0, .L30
>  .L32:
>    neg    a0, a0
> -  jal    __udivdi3    /* The dividend is hella negative.  */
> +  jal    HIDDEN_JUMPTARGET(__udivdi3)    /* The dividend is hella negative.  */
>    neg    a0, a1
>    jr     t0
>  FUNC_END (__moddi3)
> diff --git a/libgcc/config/riscv/riscv-asm.h b/libgcc/config/riscv/riscv-asm.h
> index 8550707..96dd85b 100644
> --- a/libgcc/config/riscv/riscv-asm.h
> +++ b/libgcc/config/riscv/riscv-asm.h
> @@ -33,3 +33,9 @@ X:
>  #define FUNC_ALIAS(X,Y)                \
>         .globl X;               \
>         X = Y
> +
> +#define CONCAT1(a, b)          CONCAT2(a, b)
> +#define CONCAT2(a, b)          a ## b
> +#define HIDDEN_JUMPTARGET(X)   CONCAT1(__hidden_, X)
> +#define HIDDEN_DEF(X)          FUNC_ALIAS(HIDDEN_JUMPTARGET(X), X);     \
> +                               .hidden HIDDEN_JUMPTARGET(X)
> --
> 2.7.4
>