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.

diff --git a/libgcc/config/riscv/div.S b/libgcc/config/riscv/div.S
index c9bd787..723c3b8 100644 (file)
--- 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 (file)
--- 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)