Re: Alsa-lib (libasound) segfaults on TLS variable (musl on mips)

[Szabolcs Nagy <nsz@port70.net>]

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* Szabolcs Nagy <nsz@port70.net> [2015-06-24 22:57:54 +0200]:
> the bug is that mips tls access uses a hard coded -32768
> offset relative to whatever __tls_get_addr returned.
> 
> and musl did not account for this offset.
> 

only affects mips shared objects with 'static __thread' variables,

extern __thread variables worked fine (and only those were
tested in the libc-tests).

> the attached patch fixes the issue for me,
> we will fix it in musl soon.

better patch attached that undoes the offset for extern tls
vars in relocs handling.. (and with more consistent naming)

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diff --git a/arch/mips/pthread_arch.h b/arch/mips/pthread_arch.h
index f8e35ae..904a248 100644
--- a/arch/mips/pthread_arch.h
+++ b/arch/mips/pthread_arch.h
@@ -13,4 +13,6 @@ static inline struct pthread *__pthread_self()
 #define TLS_ABOVE_TP
 #define TP_ADJ(p) ((char *)(p) + sizeof(struct pthread) + 0x7000)
 
+#define DTP_OFFSET 0x8000
+
 #define CANCEL_REG_IP (3-(union {int __i; char __b;}){1}.__b)
diff --git a/src/ldso/dynlink.c b/src/ldso/dynlink.c
index b77c6f6..b4ca410 100644
--- a/src/ldso/dynlink.c
+++ b/src/ldso/dynlink.c
@@ -337,7 +337,10 @@ static void do_relocs(struct dso *dso, size_t *rel, size_t rel_size, size_t stri
 			*reloc_addr = def.dso->tls_id;
 			break;
 		case REL_DTPOFF:
-			*reloc_addr = tls_val + addend;
+#ifndef DTP_OFFSET
+#define DTP_OFFSET 0
+#endif
+			*reloc_addr = tls_val + addend - DTP_OFFSET;
 			break;
 #ifdef TLS_ABOVE_TP
 		case REL_TPOFF:
diff --git a/src/thread/__tls_get_addr.c b/src/thread/__tls_get_addr.c
index 3633396..94ea03c 100644
--- a/src/thread/__tls_get_addr.c
+++ b/src/thread/__tls_get_addr.c
@@ -1,6 +1,10 @@
 #include <stddef.h>
 #include "pthread_impl.h"
 
+#ifndef DTP_OFFSET
+#define DTP_OFFSET 0
+#endif
+
 void *__tls_get_addr(size_t *v)
 {
 	pthread_t self = __pthread_self();
@@ -8,9 +12,9 @@ void *__tls_get_addr(size_t *v)
 	__attribute__((__visibility__("hidden")))
 	void *__tls_get_new(size_t *);
 	if (v[0]<=(size_t)self->dtv[0])
-		return (char *)self->dtv[v[0]]+v[1];
-	return __tls_get_new(v);
+		return (char *)self->dtv[v[0]]+v[1]+DTP_OFFSET;
+	return (char *)__tls_get_new(v)+DTP_OFFSET;
 #else
-	return (char *)self->dtv[1]+v[1];
+	return (char *)self->dtv[1]+v[1]+DTP_OFFSET;
 #endif
 }

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