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Message-ID: <20251208174940.949856-6-bill.roberts@arm.com>
Date: Mon, 8 Dec 2025 11:44:48 -0600
From: Bill Roberts <bill.roberts@....com>
To: musl@...ts.openwall.com
Cc: Bill Roberts <bill.roberts@....com>
Subject: [RFC 05/14] aarch64: rewrite __syscall_cp_asm in C using inline asm
Rewrite the AArch64 __syscall_cp_asm routine from assembly into
C implementations using inline assembly.
This change eliminates the need for handwritten function prologues and
epilogues in syscall_cp.s, which simplifies maintenance and allows the compiler
to automatically insert architecture features such as BTI landing pads and
pointer authentication (PAC) sequences where applicable.
Moving to C also enables the compiler to manage register allocation,
stack usage, and ABI compliance automatically while keeping the low-level
behavior (bitmasks and register accesses) explicit and verifiable.
No functional changes intended.
Signed-off-by: Bill Roberts <bill.roberts@....com>
---
src/thread/aarch64/syscall_cp.c | 61 +++++++++++++++++++++++++++++++++
src/thread/aarch64/syscall_cp.s | 32 -----------------
2 files changed, 61 insertions(+), 32 deletions(-)
create mode 100644 src/thread/aarch64/syscall_cp.c
delete mode 100644 src/thread/aarch64/syscall_cp.s
diff --git a/src/thread/aarch64/syscall_cp.c b/src/thread/aarch64/syscall_cp.c
new file mode 100644
index 00000000..d350be8f
--- /dev/null
+++ b/src/thread/aarch64/syscall_cp.c
@@ -0,0 +1,61 @@
+// __syscall_cp_asm(&self->cancel, nr, u, v, w, x, y, z)
+// x0 x1 x2 x3 x4 x5 x6 x7
+
+// syscall(nr, u, v, w, x, y, z)
+// x8 x0 x1 x2 x3 x4 x5
+
+__attribute__((visibility("hidden")))
+long __syscall_cp_asm(volatile int *cancel, long nr,
+ long a0, long a1, long a2, long a3, long a4, long a5)
+{
+ long ret;
+
+ __asm__ volatile(
+ // BEGIN marker
+ ".globl __cp_begin\n\t"
+ ".hidden __cp_begin\n\t"
+ "__cp_begin:\n\t"
+
+ "ldr w0, [x0]\n\t" // if (*cancel) goto __cp_cancel
+ "cbnz w0, __cp_cancel\n\t"
+
+ // Pack syscall args:
+ // syscall(nr, u, v, w, x, y, z)
+ // x8 x0 x1 x2 x3 x4 x5
+ // currently:
+ // x1 = nr
+ // x2..x7 = a0..a5
+ "mov x8, x1\n\t"
+ "mov x0, x2\n\t"
+ "mov x1, x3\n\t"
+ "mov x2, x4\n\t"
+ "mov x3, x5\n\t"
+ "mov x4, x6\n\t"
+ "mov x5, x7\n\t"
+ "svc #0\n"
+
+ // END marker
+ ".globl __cp_end\n\t"
+ ".hidden __cp_end\n\t"
+ "__cp_end:\n\t"
+
+ // Save syscall result from x0 into a C variable.
+ "mov %0, x0\n\t"
+ : "=r"(ret)
+ : /* all inputs are already in x0..x7 per the ABI */
+ : "x0","x1","x2","x3","x4","x5","x6","x7",
+ "x8","memory","cc"
+ );
+
+ return ret;
+}
+
+
+__attribute__((visibility("hidden")))
+long __cancel(void);
+
+__attribute__((visibility("hidden")))
+long __cp_cancel(void)
+{
+ return __cancel();
+}
diff --git a/src/thread/aarch64/syscall_cp.s b/src/thread/aarch64/syscall_cp.s
deleted file mode 100644
index 41db68af..00000000
--- a/src/thread/aarch64/syscall_cp.s
+++ /dev/null
@@ -1,32 +0,0 @@
-// __syscall_cp_asm(&self->cancel, nr, u, v, w, x, y, z)
-// x0 x1 x2 x3 x4 x5 x6 x7
-
-// syscall(nr, u, v, w, x, y, z)
-// x8 x0 x1 x2 x3 x4 x5
-
-.global __cp_begin
-.hidden __cp_begin
-.global __cp_end
-.hidden __cp_end
-.global __cp_cancel
-.hidden __cp_cancel
-.hidden __cancel
-.global __syscall_cp_asm
-.hidden __syscall_cp_asm
-.type __syscall_cp_asm,%function
-__syscall_cp_asm:
-__cp_begin:
- ldr w0,[x0]
- cbnz w0,__cp_cancel
- mov x8,x1
- mov x0,x2
- mov x1,x3
- mov x2,x4
- mov x3,x5
- mov x4,x6
- mov x5,x7
- svc 0
-__cp_end:
- ret
-__cp_cancel:
- b __cancel
--
2.51.0
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