fix local-dynamic model TLS on mips and powerpc

the TLS ABI spec for mips, powerpc, and some other (presently
unsupported) RISC archs has the return value of __tls_get_addr offset
by +0x8000 and the result of DTPOFF relocations offset by -0x8000. I
had previously assumed this part of the ABI was actually just an
implementation detail, since the adjustments cancel out. however, when
the local dynamic model is used for accessing TLS that's known to be
in the same DSO, either of the following may happen:

1. the -0x8000 offset may already be applied to the argument structure
passed to __tls_get_addr at ld time, without any opportunity for
runtime relocations.

2. __tls_get_addr may be used with a zero offset argument to obtain a
base address for the module's TLS, to which the caller then applies
immediate offsets for individual objects accessed using the local
dynamic model. since the immediate offsets have the -0x8000 adjustment
applied to them, the base address they use needs to include the
+0x8000 offset.

it would be possible, but more complex, to store the pointers in the
dtv[] array with the +0x8000 offset pre-applied, to avoid the runtime
cost of adding 0x8000 on each call to __tls_get_addr. this change
could be made later if measurements show that it would help.

diff --git a/arch/mips/pthread_arch.h b/arch/mips/pthread_arch.h
index f8e35ae46377d5f89ed3eede40dcc1cff83c2747..904a248901892bcffa572dfb6e9d5069ad96df8d 100644 (file)
--- 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/arch/powerpc/pthread_arch.h b/arch/powerpc/pthread_arch.h
index 4115ec8c2357840af373a7aa1098a7e1fac1e61a..1cbfc223ad23e3745243cf90a058ef1be75043d7 100644 (file)
--- a/arch/powerpc/pthread_arch.h
+++ b/arch/powerpc/pthread_arch.h
@@ -12,6 +12,8 @@ static inline struct pthread *__pthread_self()
 #define TLS_ABOVE_TP
 #define TP_ADJ(p) ((char *)(p) + sizeof(struct pthread) + 0x7000)
 
+#define DTP_OFFSET 0x8000
+
 // offset of the PC register in mcontext_t, divided by the system wordsize
 // the kernel calls the ip "nip", it's the first saved value after the 32
 // GPRs.

diff --git a/src/internal/pthread_impl.h b/src/internal/pthread_impl.h
index e29f9c82e421066db958d21aa0adb7ce2abc5b83..3890bb56fb4d122db323e513460a4c045666d741 100644 (file)
--- a/src/internal/pthread_impl.h
+++ b/src/internal/pthread_impl.h
@@ -94,6 +94,10 @@ struct __timer {
 #define CANARY canary
 #endif
 
+#ifndef DTP_OFFSET
+#define DTP_OFFSET 0
+#endif
+
 #define SIGTIMER 32
 #define SIGCANCEL 33
 #define SIGSYNCCALL 34

diff --git a/src/ldso/dynlink.c b/src/ldso/dynlink.c
index b77c6f6b9c8c1dcce7acea8d5bee7128f501ef6d..d2a72492e7212b45b4f3090c40f55a52728c780a 100644 (file)
--- a/src/ldso/dynlink.c
+++ b/src/ldso/dynlink.c
@@ -337,7 +337,7 @@ 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;
+                       *reloc_addr = tls_val + addend - DTP_OFFSET;
                        break;
 #ifdef TLS_ABOVE_TP
                case REL_TPOFF:
@@ -1102,7 +1102,7 @@ void *__tls_get_new(size_t *v)
        __block_all_sigs(&set);
        if (v[0]<=(size_t)self->dtv[0]) {
                __restore_sigs(&set);
-               return (char *)self->dtv[v[0]]+v[1];
+               return (char *)self->dtv[v[0]]+v[1]+DTP_OFFSET;
        }
 
        /* This is safe without any locks held because, if the caller
@@ -1135,7 +1135,7 @@ void *__tls_get_new(size_t *v)
                if (p->tls_id == v[0]) break;
        }
        __restore_sigs(&set);
-       return mem + v[1];
+       return mem + v[1] + DTP_OFFSET;
 }
 
 static void update_tls_size()

diff --git a/src/thread/__tls_get_addr.c b/src/thread/__tls_get_addr.c
index 36333967bee9b237d5a006bf435d8a2976ba30f0..84a413d4a8cd4be9bdd662b66d10c6fe877bc76b 100644 (file)
--- a/src/thread/__tls_get_addr.c
+++ b/src/thread/__tls_get_addr.c
@@ -8,9 +8,9 @@ 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 (char *)self->dtv[v[0]]+v[1]+DTP_OFFSET;
        return __tls_get_new(v);
 #else
-       return (char *)self->dtv[1]+v[1];
+       return (char *)self->dtv[1]+v[1]+DTP_OFFSET;
 #endif
 }