[musl] arm32 tlsdesc bug

[Rui Ueyama <rui314@gmail.com>]

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Hi,

I think there's a bug in musl's TLSDESC implementation for ARM32.

TLSDESC uses two consecutive GOT slots to store a function pointer and its
argument. Usually, the function pointer is stored in the first slot and the
argument in the second. However, on ARM32, the order is reversed; the
argument is stored in the first slot.

If a TLSDESC relocation has a non-zero addend, it's applied to the function
argument and not to the function pointer. That means, for an ABI that uses
the REL-type relocations (as opposed to RELA-type), the addend should be
stored to the location where the function argument is stored, and that's
the first slot on ARM32.

So, I believe we need something like this.

diff --git a/ldso/dynlink.c b/ldso/dynlink.c
index ceca3c98..254fa5b8 100644
--- a/ldso/dynlink.c
+++ b/ldso/dynlink.c
@@ -513,11 +513,17 @@ static void do_relocs(struct dso *dso, size_t *rel,
size_t rel_size, size_t stri
                case REL_TPOFF_NEG:
                        *reloc_addr = def.dso->tls.offset - tls_val +
addend;
                        break;
 #endif
                case REL_TLSDESC:
-                       if (stride<3) addend = reloc_addr[1];
+                       if (stride<3) {
+#ifdef TLSDESC_BACKWARDS
+                               addend = reloc_addr[0];
+#else
+                               addend = reloc_addr[1];
+#endif
+                       }
                        if (def.dso->tls_id > static_tls_cnt) {
                                struct td_index *new = malloc(sizeof *new);
                                if (!new) {
                                        error(
                                        "Error relocating %s: cannot
allocate TLSDESC for %s",

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