Commit 91fa2c61aacd002228c37cb651fa0a350bd7ac59 | zig

author	Alex Rønne Petersen <alex@alexrp.com> 2025-10-03 03:22:02+02:00
committer	Alex Rønne Petersen <alex@alexrp.com> 2025-10-03 03:29:20+02:00
log	91fa2c61aacd002228c37cb651fa0a350bd7ac59
tree	75efed76fbc47b7383e2fb50137bab00f962707f
parent	bc4da9a90743c11c7c0b3e485f46d365d57d87b7
signature	Signed by SSH key SHA256:7B/LJ7bpR1eX8aCXSr4mtd5M45VMPKcx9zY8e95b5QM

compiler: control the s390x backchain feature through the frame pointer option

This is a little different from how C/C++ compilers do this, but I think it's
justified because it's what users actually *mean* when the use frame pointer
options.

This is another one of those LLVM "CPU" features that have nothing to do with
CPU at all and should really be a TargetMachine option or something. One day
we'll figure out a better way of dealing with these...

2 files changed, 10 insertions(+), 3 deletions(-)

src
- Compilation.zig
- Package
  - Module.zig

src/Compilation.zig+6-2

 @@ -7193,6 +7193,9 @@ pub fn addCCArgs(
         }
         try argv.append(if (mod.omit_frame_pointer) "-fomit-frame-pointer" else "-fno-omit-frame-pointer");
+        if (target.cpu.arch == .s390x) {
+            try argv.append(if (mod.omit_frame_pointer) "-mbackchain" else "-mno-backchain");
+        }
         const ssp_buf_size = mod.stack_protector;
         if (ssp_buf_size != 0) {
 @@ -7258,9 +7261,10 @@ pub fn addCCArgs(
                 const is_enabled = target.cpu.features.isEnabled(index);
                 if (feature.llvm_name) |llvm_name| {
-                    // We communicate float ABI to Clang through the dedicated options.
+                    // We communicate these to Clang through the dedicated options.
                     if (std.mem.startsWith(u8, llvm_name, "soft-float") or
-                        std.mem.startsWith(u8, llvm_name, "hard-float"))
+                        std.mem.startsWith(u8, llvm_name, "hard-float") or
+                        (target.cpu.arch == .s390x and std.mem.eql(u8, llvm_name, "backchain")))
                         continue;
                     // Ignore these until we figure out how to handle the concept of omitting features.

src/Package/Module.zig+4-1

 @@ -343,7 +343,10 @@ pub fn create(arena: Allocator, options: CreateOptions) !*Package.Module {
                 // See https://github.com/ziglang/zig/issues/23539
                 if (target_util.isDynamicAMDGCNFeature(target, feature)) continue;
-                const is_enabled = target.cpu.features.isEnabled(feature.index);
+                var is_enabled = target.cpu.features.isEnabled(feature.index);
+                if (target.cpu.arch == .s390x and @as(std.Target.s390x.Feature, @enumFromInt(feature.index)) == .backchain) {
+                    is_enabled = !omit_frame_pointer;
+                }
                 if (is_enabled) {
                     try buf.ensureUnusedCapacity(2 + llvm_name.len);