Export __global_pointer$ from executable

RISC-V psABI requires that symbol to be exported from an executable
if there's a GP-relative reference. For simplicity, we always export
it from executable as long as it has a .dynamic section.

#1222

elf/passes.cc

@@ -801,8 +801,11 @@ void add_synthetic_symbols(Context<E> &ctx) {
   if constexpr (supports_tlsdesc<E>)
     ctx._TLS_MODULE_BASE_ = add("_TLS_MODULE_BASE_", STT_TLS);
 
-  if constexpr (is_riscv<E>)
+  if constexpr (is_riscv<E>) {
     ctx.__global_pointer = add("__global_pointer$");
+    if (ctx.dynamic && !ctx.arg.shared)
+      ctx.__global_pointer->is_exported = true;
+  }
 
   if constexpr (is_arm32<E>) {
     ctx.__exidx_start = add("__exidx_start");

test/elf/riscv64_global-pointer.sh

@@ -0,0 +1,27 @@
+#!/bin/bash
+. $(dirname $0)/common.inc
+
+cat <<EOF | $CC -o $t/a.o -c -xc - -fPIC
+#include <stdio.h>
+int main() {
+  printf("Hello world\n");
+}
+EOF
+
+$CC -B. -o $t/exe1 $t/a.o -fno-PIE
+readelf -W --dyn-syms $t/exe1 | grep -Fq '__global_pointer$'
+
+$CC -B. -o $t/exe2 $t/a.o -fPIE
+readelf -W --dyn-syms $t/exe2 | grep -Fq '__global_pointer$'
+
+
+cat <<EOF | $CC -o $t/b.o -c -xc - -fPIC
+#include <stdio.h>
+int hello() {
+  printf("Hello world\n");
+}
+EOF
+
+$CC -B. -o $t/c.so $t/b.o -shared
+readelf -W --dyn-syms $t/c.so > $t/log1
+! grep -Fq '__global_pointer$' $t/log1 || false