[PATCH] fix tls offsets when p_vaddr%p_align != 0 for TLS_ABOVE_TP

[Szabolcs Nagy <nsz@port70.net>]

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this came up because lld changed tls alignment on aarch64 as a
workaround for a bionic abi issue https://reviews.llvm.org/D53906
but lld does not handle p_vaddr%p_align!=0 right so it broke on glibc
https://reviews.llvm.org/D61824

the patch is untested (bfd linker cannot seem to create problematic
elf objects), but at least there are no regressions with libc-test.

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From 8c94fcbc9faeb8b07132506757c3d3973652420e Mon Sep 17 00:00:00 2001
From: Szabolcs Nagy <nsz@port70.net>
Date: Mon, 13 May 2019 18:47:11 +0000
Subject: [PATCH] fix tls offsets when p_vaddr%p_align != 0 for TLS_ABOVE_TP

currently the bfd linker does not seem to create tls segments where
p_vaddr%p_align != 0, but this is valid in ELF and then the runtime
computed tls offset must satisfy

  offset%p_align == (base+p_vaddr)%p_align

and in case of local exec tls (main executable) the smallest such
offset must be used (otherwise it is incompatible with the offset
computed by the static linker). the !TLS_ABOVE_TP case handled this
correctly (the offset is negative then in the formula).

the ldso code for TLS_ABOVE_TP is changed so the static tls offset
of each module satisfies the formula and tls_offset always points
to the end of the allocated static tls area (and not aligned up to
tls_align or MIN_TLS_ALIGN). the tls_offset computation was wrong
when multiple modules were loaded with static tls and in some the
tls segment p_memsz%p_align != 0.
---
 ldso/dynlink.c       | 13 ++++++-------
 src/env/__init_tls.c |  3 ++-
 2 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/ldso/dynlink.c b/ldso/dynlink.c
index 42a5470d..6dc39483 100644
--- a/ldso/dynlink.c
+++ b/ldso/dynlink.c
@@ -1126,9 +1126,9 @@ static struct dso *load_library(const char *name, struct dso *needed_by)
 		p->tls_id = ++tls_cnt;
 		tls_align = MAXP2(tls_align, p->tls.align);
 #ifdef TLS_ABOVE_TP
-		p->tls.offset = tls_offset + ( (tls_align-1) &
-			-(tls_offset + (uintptr_t)p->tls.image) );
-		tls_offset += p->tls.size;
+		p->tls.offset = tls_offset + ( (p->tls.align-1) &
+			(-tls_offset + (uintptr_t)p->tls.image) );
+		tls_offset = p->tls.offset + p->tls.size;
 #else
 		tls_offset += p->tls.size + p->tls.align - 1;
 		tls_offset -= (tls_offset + (uintptr_t)p->tls.image)
@@ -1797,10 +1797,9 @@ _Noreturn void __dls3(size_t *sp)
 		app.tls_id = tls_cnt = 1;
 #ifdef TLS_ABOVE_TP
 		app.tls.offset = GAP_ABOVE_TP;
-		app.tls.offset += -GAP_ABOVE_TP & (app.tls.align-1);
-		tls_offset = app.tls.offset + app.tls.size
-			+ ( -((uintptr_t)app.tls.image + app.tls.size)
-			& (app.tls.align-1) );
+		app.tls.offset += (-GAP_ABOVE_TP + (uintptr_t)app.tls.image)
+			& (app.tls.align-1);
+		tls_offset = app.tls.offset + app.tls.size;
 #else
 		tls_offset = app.tls.offset = app.tls.size
 			+ ( -((uintptr_t)app.tls.image + app.tls.size)
diff --git a/src/env/__init_tls.c b/src/env/__init_tls.c
index 5f12500c..772baba3 100644
--- a/src/env/__init_tls.c
+++ b/src/env/__init_tls.c
@@ -115,7 +115,8 @@ static void static_init_tls(size_t *aux)
 		& (main_tls.align-1);
 #ifdef TLS_ABOVE_TP
 	main_tls.offset = GAP_ABOVE_TP;
-	main_tls.offset += -GAP_ABOVE_TP & (main_tls.align-1);
+	main_tls.offset += (-GAP_ABOVE_TP + (uintptr_t)main_tls.image)
+		& (main_tls.align-1);
 #else
 	main_tls.offset = main_tls.size;
 #endif
-- 
2.21.0