Re: [PATCH v4 2/6] powerpc/module: Handle caller-saved TOC in module linker

On Tue, 2022-10-25 at 13:10 +1100, Andrew Donnellan wrote:

On Mon, 2022-10-10 at 11:29 +1100, Benjamin Gray wrote:

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A function symbol may set a value in the st_other field to
indicate
the TOC should be treated as caller-saved. The linker should
ensure> the
current TOC is saved before calling it and restore the TOC>
afterwards,
much like external calls.

As I suggested on the last revision, worth mentioning here that it's
the '.localentry <NAME>, 1' directive we're talking about here.

Ah right, whoops. Added "For example, GCC and Clang support a
'.localentry <NAME>, 1' directive to set this explicitly in assembly."

The exact method for doing this seems to be nonstandard (GCC supports
arbitrary value in 1--7, Clang special cases only 1), so originally I
was avoiding specifying how it is set.

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@@ -632,7 +643,8 @@ int apply_relocate_add(Elf64_Shdr *sechdrs,

                case R_PPC_REL24:
                        /* FIXME: Handle weak symbols here --RR
*/
                        if (sym->st_shndx == SHN_UNDEF ||
-                           sym->st_shndx == SHN_LIVEPATCH) {
+                           sym->st_shndx == SHN_LIVEPATCH ||
+                           need_r2save_stub(sym->st_other)) {
                                /* External: go via stub */

Perhaps this comment should be updated to mention that there are non-
external but external-like calls?

Otherwise

Reviewed-by: Andrew Donnellan <redacted>

Updated to "/* May use different / not preserve TOC: go via stub */",
will add your reviewed-by in the next version. For now I'll wait for
any other feedback before sending it.

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