From: Mark Wooding <mdw@distorted.org.uk>
Date: Sun, 11 Oct 2020 23:18:15 +0000 (+0100)
Subject: base/regdump-arm64.S, base/regdump.h: Save NZCV and x8--x15 early.
X-Git-Url: https://git.distorted.org.uk/~mdw/catacomb/commitdiff_plain/818bad9b1b5e68bdd26595a0ec5f513fe56ba174

base/regdump-arm64.S, base/regdump.h: Save NZCV and x8--x15 early.

Alas, the processor flags /and/ at least x14 and x15 are clobbered by
the PLT on-demand linkage machinery, so we must save them in the macro
before calling out to the library.  To be safe, preserve all of the
non-argument call-clobbered registers.
---

diff --git a/base/regdump-arm64.S b/base/regdump-arm64.S
index 81c9f8e7..183d38f0 100644
--- a/base/regdump-arm64.S
+++ b/base/regdump-arm64.S
@@ -56,10 +56,6 @@ FUNC(regdump_gpsave)
 	stp	x2, x3, [sp, #16]
 	stp	x4, x5, [sp, #32]
 	stp	x6, x7, [sp, #48]
-	stp	x8, x9, [sp, #64]
-	stp	x10, x11, [sp, #80]
-	stp	x12, x13, [sp, #96]
-	stp	x14, x15, [sp, #112]
 	stp	x18, x19, [sp, #144]
 	stp	x20, x21, [sp, #160]
 	stp	x22, x23, [sp, #176]
@@ -73,10 +69,6 @@ FUNC(regdump_gpsave)
 	add	x0, x20, #REGDUMP_GPSIZE
 	str	x0, [x20, #31*8]
 
-	// Capture the status flags.
-	mrs	x0, nzcv
-	str	x0, [x20, #8*REGIX_NZCV]
-
 	// Set the return address as our PC.
 	str	x30, [x20, #8*REGIX_PC]
 
diff --git a/base/regdump.h b/base/regdump.h
index a07072df..3a6d59cb 100644
--- a/base/regdump.h
+++ b/base/regdump.h
@@ -774,8 +774,15 @@ DO32(REGDEF_FP)
 	// Make space for the register save area.
 	sub	sp, sp, #REGDUMP_GPSIZE
 
-	// Save flags and general-purpose registers.
-	stp	x16, x17, [sp, #8*16]
+	// Save flags and general-purpose registers.  The PLT linkage code
+	// makes free with x8--x17, so we must save those here.
+	mrs	x30, nzcv
+	str	x30, [sp, #8*REGIX_NZCV]
+	stp	x8, x9, [sp, #64]
+	stp	x10, x11, [sp, #80]
+	stp	x12, x13, [sp, #96]
+	stp	x14, x15, [sp, #112]
+	stp	x16, x17, [sp, #128]
 	bl	regdump_gpsave
 
 	// Make space for the extended registers.