82 lines
2.9 KiB
Diff
82 lines
2.9 KiB
Diff
From 946167906ed8646c433c257b074a10e01f0a7dab Mon Sep 17 00:00:00 2001
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From: "Paul E. Murphy" <murp@ibm.com>
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Date: Tue, 22 Mar 2022 11:52:02 -0500
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Subject: [PATCH] runtime: make static/dynamic startup detection work with musl
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on ppc64le
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The glibc loader explicitly sets the first doubleword on the stack (R1)
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to $0 to indicate it was dynamically loaded.
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An ELFv2 ABI compliant loader will set R3/R4 to argc/argv when starting
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the process, and R13 to TLS. musl is not compliant. Instead it passes
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argc/argv like the kernel, but R3/R4 are in an undefined state and R13
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is valid.
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With the knowledge above, the startup code can be modified to
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dynamically handle all three cases when linked internally.
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Fixes #51787
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Change-Id: I5de33862c161900d9161817388bbc13a65fdc69c
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Reviewed-on: https://go-review.googlesource.com/c/go/+/394654
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Reviewed-by: Cherry Mui <cherryyz@google.com>
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Run-TryBot: Paul Murphy <murp@ibm.com>
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TryBot-Result: Gopher Robot <gobot@golang.org>
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Trust: Paul Murphy <murp@ibm.com>
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Trust: Lynn Boger <laboger@linux.vnet.ibm.com>
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---
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src/runtime/rt0_linux_ppc64le.s | 32 +++++++++++++++++++++-----------
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1 file changed, 21 insertions(+), 11 deletions(-)
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diff --git a/src/runtime/rt0_linux_ppc64le.s b/src/runtime/rt0_linux_ppc64le.s
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index 4f7c6e6c99f6..66f7e7b22a41 100644
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--- a/go/src/runtime/rt0_linux_ppc64le.s
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+++ b/go/src/runtime/rt0_linux_ppc64le.s
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@@ -147,25 +147,35 @@ TEXT _main<>(SB),NOSPLIT,$-8
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// In a statically linked binary, the stack contains argc,
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// argv as argc string pointers followed by a NULL, envv as a
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// sequence of string pointers followed by a NULL, and auxv.
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- // There is no TLS base pointer.
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+ // The TLS pointer should be initialized to 0.
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//
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- // In a dynamically linked binary, r3 contains argc, r4
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- // contains argv, r5 contains envp, r6 contains auxv, and r13
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+ // In an ELFv2 compliant dynamically linked binary, R3 contains argc,
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+ // R4 contains argv, R5 contains envp, R6 contains auxv, and R13
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// contains the TLS pointer.
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//
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- // Figure out which case this is by looking at r4: if it's 0,
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- // we're statically linked; otherwise we're dynamically
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- // linked.
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- CMP R0, R4
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- BNE dlink
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-
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- // Statically linked
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+ // When loading via glibc, the first doubleword on the stack points
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+ // to NULL a value. (that is *(uintptr)(R1) == 0). This is used to
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+ // differentiate static vs dynamicly linked binaries.
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+ //
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+ // If loading with the musl loader, it doesn't follow the ELFv2 ABI. It
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+ // passes argc/argv similar to the linux kernel, R13 (TLS) is
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+ // initialized, and R3/R4 are undefined.
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+ MOVD (R1), R12
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+ CMP R0, R12
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+ BEQ tls_and_argcv_in_reg
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+
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+ // Arguments are passed via the stack (musl loader or a static binary)
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MOVD 0(R1), R3 // argc
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ADD $8, R1, R4 // argv
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+
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+ // Did the TLS pointer get set? If so, don't change it (e.g musl).
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+ CMP R0, R13
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+ BNE tls_and_argcv_in_reg
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+
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MOVD $runtime·m0+m_tls(SB), R13 // TLS
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ADD $0x7000, R13
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-dlink:
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+tls_and_argcv_in_reg:
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BR main(SB)
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TEXT main(SB),NOSPLIT,$-8
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