File libpulp-0002-Non-ABI-compliant-__tls_get_addr-f... of Package glibc

Overview Repositories Revisions Requests Users Attributes Meta

File libpulp-0002-Non-ABI-compliant-__tls_get_addr-for-libpulp.patch of Package glibc (Revision 6b2f75cc6926c50cd63dc94e39661334)

Currently displaying revision 6b2f75cc6926c50cd63dc94e39661334 , Show latest

From 213173363bfebd10d14f5a9027582b938ad4b085 Mon Sep 17 00:00:00 2001
From: "Gabriel F. T. Gomes" <gagomes@suse.de>
Date: Fri, 24 Jul 2020 11:10:25 -0300
Subject: [PATCH 2/2] Non ABI-compliant __tls_get_addr for libpulp

Userspace live-patching enabled libraries track all calls into the
library via the __ulp_entry function.  This tracking is per-thread, so
it uses thread-local variables, which require calls into __tls_get_addr.
On the hot-path, few registers are used, however, on the slow path, it
calls a function in C, so the ABI must be strictly followed.

This patch adds a new function, which can be called from __ulp_entry
without saving caller-save registers. If the hot-path finds the address,
it returns quickly. Otherwise, it saves the registers that __ulp_entry
did not save, and calls the slow C function.
---
 elf/Versions                                 |  4 ++
 sysdeps/unix/sysv/linux/x86_64/64/ld.abilist |  1 +
 sysdeps/x86_64/tls_get_addr.S                | 63 ++++++++++++++++++++
 3 files changed, 68 insertions(+)

diff --git a/elf/Versions b/elf/Versions
index c0f59185e8..f075c579d8 100644
--- a/elf/Versions
+++ b/elf/Versions
@@ -77,5 +77,9 @@ ld {
   GLIBC_LIBPULP1 {
     # Libpulp checks to avoid deadlock in AS-Unsafe functions.
     __libpulp_dlopen_checks;
+
+    # Non ABI-compliant version of __tls_get_addr to avoid the need of
+    # saving/restoring registers on the fast path.
+    __libpulp_tls_get_addr;
   }
 }
diff --git a/sysdeps/unix/sysv/linux/x86_64/64/ld.abilist b/sysdeps/unix/sysv/linux/x86_64/64/ld.abilist
index 861962ed19..08da57de8f 100644
--- a/sysdeps/unix/sysv/linux/x86_64/64/ld.abilist
+++ b/sysdeps/unix/sysv/linux/x86_64/64/ld.abilist
@@ -11,3 +11,4 @@ GLIBC_2.3 __tls_get_addr F
 GLIBC_2.4 GLIBC_2.4 A
 GLIBC_LIBPULP1 GLIBC_LIBPULP1 A
 GLIBC_LIBPULP1 __libpulp_dlopen_checks F
+GLIBC_LIBPULP1 __libpulp_tls_get_addr F
diff --git a/sysdeps/x86_64/tls_get_addr.S b/sysdeps/x86_64/tls_get_addr.S
index 9d38fb3be5..09c69314de 100644
--- a/sysdeps/x86_64/tls_get_addr.S
+++ b/sysdeps/x86_64/tls_get_addr.S
@@ -58,4 +58,67 @@ ENTRY (__tls_get_addr)
 	cfi_def_cfa (%rsp, 8)
 	ret
 END (__tls_get_addr)
+
+/* Userspace live-patching enabled libraries track all calls into the
+   library via the __ulp_entry function.  This tracking is per-thread,
+   so it uses thread-local variables, which require calls into
+   __tls_get_addr.  On the hot-path, few registers are used, however,
+   on the slow path, it calls a function in C, so the ABI must be
+   strictly followed.
+
+   This new function can be called from __ulp_entry without saving
+   caller-save registers. If the hot-path finds the address, it returns
+   quickly. Otherwise, it saves the registers that __ulp_entry did not
+   save, and calls the slow C function.  */
+ENTRY (__libpulp_tls_get_addr)
+	pushq	%rdx
+	mov	%fs:DTV_OFFSET, %RDX_LP
+	mov	GL_TLS_GENERATION_OFFSET+_rtld_local(%rip), %RAX_LP
+	/* GL(dl_tls_generation) == dtv[0].counter */
+	cmp	%RAX_LP, (%rdx)
+	jne	1f
+	mov	TI_MODULE_OFFSET(%rdi), %RAX_LP
+	/* dtv[ti->ti_module] */
+# ifdef __LP64__
+	salq	$4, %rax
+	movq	(%rdx,%rax), %rax
+# else
+	movl	(%rdx,%rax, 8), %eax
+# endif
+	cmp	$-1, %RAX_LP
+	je	1f
+	add	TI_OFFSET_OFFSET(%rdi), %RAX_LP
+	popq	%rdx
+	ret
+
+1:
+	/* Push everything that __ulp_entry had not.  */
+	pushq	%r10
+	pushq	%r9
+	pushq	%r8
+	pushq	%rsi
+	pushq	%rcx
+
+	/* On the slow path, align the stack.  */
+	pushq	%rbp
+	cfi_def_cfa_offset (16)
+	cfi_offset (%rbp, -16)
+	mov	%RSP_LP, %RBP_LP
+	cfi_def_cfa_register (%rbp)
+	and	$-16, %RSP_LP
+	call	__tls_get_addr_slow
+	mov	%RBP_LP, %RSP_LP
+	popq	%rbp
+	cfi_def_cfa (%rsp, 8)
+
+	/* Restore register before returning to __ulp_entry.  */
+	popq	%rcx
+	popq	%rsi
+	popq	%r8
+	popq	%r9
+	popq	%r10
+	popq	%rdx
+
+	ret
+END (__libpulp_tls_get_addr)
 #endif /* SHARED */
-- 
2.28.0

Places

File libpulp-0002-Non-ABI-compliant-__tls_get_addr-for-libpulp.patch of Package glibc (Revision 6b2f75cc6926c50cd63dc94e39661334)

Places