[binutils-gdb] PowerPC: fix external calls from modules built by the compile command

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=a6d0eb39462588ed757cb1fe97749863604588ff

commit a6d0eb39462588ed757cb1fe97749863604588ff
Author: Abhay Kandpal <[email protected]>
Date:   Thu Aug 20 07:03:57 2026 -0500

    PowerPC: fix external calls from modules built by the compile command
    
    A module built for the compile command is loaded into inferior memory
    without a linker, so it has no PLT.  On ELFv2 the default code model
    still emits a direct bl for a call to another module, leaving r12 unset
    and the caller's TOC pointer unrestored, and the callee then derives a
    wrong r2 from a stale r12.
    
    gdb.compile/compile-setjmp.exp shows this: the injected code calls
    setjmp, whose global entry point computes r2 from a stale r12, and the
    first TOC-relative load segfaults.
    
    -mlongcall makes the call indirect, but on its own it reaches the target
    through a PLT entry, giving R_PPC64_PLT16_HA/LO_DS relocations that BFD's
    generic linker rejects.  Adding -mno-pltseq resolves the call against the
    module's own TOC instead, via R_PPC64_TOC16_HA/LO_DS, which GDB already
    handles.  GCC then emits the r2 save and restore around the call itself.
    
    Tested on powerpc64le-linux; the two compile-setjmp.exp failures now pass
    with no unexpected failures in the full testsuite.
    
    gdb/
            * ppc-linux-tdep.c (ppc64_gcc_target_options): New function.
            (ppc_linux_init_abi): Set gcc_target_options for ELFv2.
    
    Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=34551
    Suggested-by: Ulrich Weigand <[email protected]>

Diff:
---
 gdb/ppc-linux-tdep.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/gdb/ppc-linux-tdep.c b/gdb/ppc-linux-tdep.c
index 8a55ff5d4af..b468dbcb62c 100644
--- a/gdb/ppc-linux-tdep.c
+++ b/gdb/ppc-linux-tdep.c
@@ -2196,6 +2196,18 @@ rs6000_linux_adjust_frame_regnum (struct gdbarch *gdbarch, int num,
   return num;
 }
 
+/* Implement gdbarch_gcc_target_options.  A module built for the "compile"
+   command is loaded into inferior memory without a linker, so it has no
+   PLT.  -mlongcall makes calls to other modules indirect, and -mno-pltseq
+   stops GCC reaching the target through a PLT entry; together they let the
+   call be resolved against the module's own TOC.  */
+
+static std::string
+ppc64_gcc_target_options (struct gdbarch *gdbarch)
+{
+  return default_gcc_target_options (gdbarch) + " -mlongcall -mno-pltseq";
+}
+
 static void
 ppc_linux_init_abi (struct gdbarch_info info,
 		    struct gdbarch *gdbarch)
@@ -2304,6 +2316,7 @@ ppc_linux_init_abi (struct gdbarch_info info,
 	    (gdbarch, ppc_elfv2_elf_make_msymbol_special);
 
 	  set_gdbarch_skip_entrypoint (gdbarch, ppc_elfv2_skip_entrypoint);
+	  set_gdbarch_gcc_target_options (gdbarch, ppc64_gcc_target_options);
 	}
 
       /* Shared library handling.  */