zig

commit 63aa85e7afb37d0b2b5c48309ef1a88d8fd444b5 (tree)
parent 8ea323822ba1fc2f54940841b2cedb3494230a3c
Author: Andrew Kelley <andrew@ziglang.org>
Date:   Thu,  1 Aug 2024 00:47:05 -0700

Merge pull request #20872 from alexrp/riscv-gp

start: Initialize `gp` to `__global_pointer$` on riscv.
Diffstat:
M
lib/std/start.zig
 | 
17
+++++++++++++++--

1 file changed, 15 insertions(+), 2 deletions(-)
diff --git a/lib/std/start.zig b/lib/std/start.zig
@@ -272,13 +272,27 @@ fn _start() callconv(.Naked) noreturn {
             \\ bstrins.d $sp, $zero, 3, 0
             \\ b %[posixCallMainAndExit]
             ,
+            // zig fmt: off
             .riscv32, .riscv64 =>
+            // The self-hosted riscv64 backend is not able to assemble this yet.
+            if (builtin.zig_backend != .stage2_riscv64)
+                // The RISC-V ELF ABI assumes that `gp` is set to the value of `__global_pointer$` at
+                // startup in order for GP relaxation to work, even in static builds.
+                \\ .weak __global_pointer$
+                \\ .hidden __global_pointer$
+                \\ .option push
+                \\ .option norelax
+                \\ lla gp, __global_pointer$
+                \\ .option pop
+            else ""
+            ++
             \\ li s0, 0
             \\ li ra, 0
             \\ mv a0, sp
             \\ andi sp, sp, -16
             \\ tail %[posixCallMainAndExit]@plt
             ,
+            // zig fmt: off
             .m68k =>
             // Note that the - 8 is needed because pc in the jsr instruction points into the middle
             // of the jsr instruction. (The lea is 6 bytes, the jsr is 4 bytes.)
@@ -293,6 +307,7 @@ fn _start() callconv(.Naked) noreturn {
             \\ .gpword .
             \\ .gpword %[posixCallMainAndExit]
             \\ 1:
+            // The `gp` register on MIPS serves a similar purpose to `r2` (ToC pointer) on PPC64.
             \\ lw $gp, 0($ra)
             \\ subu $gp, $ra, $gp
             \\ lw $25, 4($ra)
@@ -314,8 +329,6 @@ fn _start() callconv(.Naked) noreturn {
             \\ .gpdword %[posixCallMainAndExit]
             \\ 1:
             // The `gp` register on MIPS serves a similar purpose to `r2` (ToC pointer) on PPC64.
-            // We need to set it up in order for dynamically-linked / position-independent code to
-            // work.
             \\ ld $gp, 0($ra)
             \\ dsubu $gp, $ra, $gp
             \\ ld $25, 8($ra)