linux-kernel - [tip: objtool/core] x86/unwind/orc: Change REG_SP

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Date:   Wed, 10 Feb 2021 20:01:24 -0000
From:   "tip-bot2 for Peter Zijlstra" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Miroslav Benes <mbenes@...e.cz>,
        Josh Poimboeuf <jpoimboe@...hat.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: objtool/core] x86/unwind/orc: Change REG_SP_INDIRECT

The following commit has been merged into the objtool/core branch of tip:

Commit-ID:     87ccc826bf1c9e5ab4c2f649b404e02c63e47622
Gitweb:        https://git.kernel.org/tip/87ccc826bf1c9e5ab4c2f649b404e02c63e47622
Author:        Peter Zijlstra <peterz@...radead.org>
AuthorDate:    Wed, 03 Feb 2021 12:02:21 +01:00
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Wed, 10 Feb 2021 20:53:51 +01:00

x86/unwind/orc: Change REG_SP_INDIRECT

Currently REG_SP_INDIRECT is unused but means (%rsp + offset),
change it to mean (%rsp) + offset.

The reason is that we're going to swizzle stack in the middle of a C
function with non-trivial stack footprint. This means that when the
unwinder finds the ToS, it needs to dereference it (%rsp) and then add
the offset to the next frame, resulting in: (%rsp) + offset

This is somewhat unfortunate, since REG_BP_INDIRECT is used (by DRAP)
and thus needs to retain the current (%rbp + offset).

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Reviewed-by: Miroslav Benes <mbenes@...e.cz>
Acked-by: Josh Poimboeuf <jpoimboe@...hat.com>
---
 arch/x86/kernel/unwind_orc.c | 5 ++++-
 tools/objtool/orc_dump.c     | 2 +-
 2 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/unwind_orc.c b/arch/x86/kernel/unwind_orc.c
index 73f8001..2a1d47f 100644
--- a/arch/x86/kernel/unwind_orc.c
+++ b/arch/x86/kernel/unwind_orc.c
@@ -471,7 +471,7 @@ bool unwind_next_frame(struct unwind_state *state)
 		break;
 
 	case ORC_REG_SP_INDIRECT:
-		sp = state->sp + orc->sp_offset;
+		sp = state->sp;
 		indirect = true;
 		break;
 
@@ -521,6 +521,9 @@ bool unwind_next_frame(struct unwind_state *state)
 	if (indirect) {
 		if (!deref_stack_reg(state, sp, &sp))
 			goto err;
+
+		if (orc->sp_reg == ORC_REG_SP_INDIRECT)
+			sp += orc->sp_offset;
 	}
 
 	/* Find IP, SP and possibly regs: */
diff --git a/tools/objtool/orc_dump.c b/tools/objtool/orc_dump.c
index c53fae9..f5a8508 100644
--- a/tools/objtool/orc_dump.c
+++ b/tools/objtool/orc_dump.c
@@ -55,7 +55,7 @@ static void print_reg(unsigned int reg, int offset)
 	if (reg == ORC_REG_BP_INDIRECT)
 		printf("(bp%+d)", offset);
 	else if (reg == ORC_REG_SP_INDIRECT)
-		printf("(sp%+d)", offset);
+		printf("(sp)%+d", offset);
 	else if (reg == ORC_REG_UNDEFINED)
 		printf("(und)");
 	else