linux-kernel - [PATCH v1 10/11] tools/nolibc: riscv: shrink _start with _start

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Message-Id: <4a6e7245c3aa07eb20fd6c6aa43bc663e480e0c5.1687976753.git.falcon@tinylab.org>
Date:   Thu, 29 Jun 2023 03:04:12 +0800
From:   Zhangjin Wu <falcon@...ylab.org>
To:     thomas@...ch.de, w@....eu
Cc:     falcon@...ylab.org, arnd@...db.de, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org, linux-riscv@...ts.infradead.org
Subject: [PATCH v1 10/11] tools/nolibc: riscv: shrink _start with _start_c

Let's move most of the _start operations to _start_c().

Signed-off-by: Zhangjin Wu <falcon@...ylab.org>
---
 tools/include/nolibc/arch-riscv.h | 42 ++++---------------------------
 1 file changed, 5 insertions(+), 37 deletions(-)

diff --git a/tools/include/nolibc/arch-riscv.h b/tools/include/nolibc/arch-riscv.h
index 7f4abcc15206..ec0f9c597d0b 100644
--- a/tools/include/nolibc/arch-riscv.h
+++ b/tools/include/nolibc/arch-riscv.h
@@ -9,18 +9,6 @@
 
 #include "compiler.h"
 
-#if   __riscv_xlen == 64
-#define PTRLOG "3"
-#define SZREG  "8"
-#define REG_L  "ld"
-#define REG_S  "sd"
-#elif __riscv_xlen == 32
-#define PTRLOG "2"
-#define SZREG  "4"
-#define REG_L  "lw"
-#define REG_S  "sw"
-#endif
-
 /* Syscalls for RISCV :
  *   - stack is 16-byte aligned
  *   - syscall number is passed in a7
@@ -153,40 +141,20 @@
 	_arg1;									\
 })
 
-char **environ __attribute__((weak));
-const unsigned long *_auxv __attribute__((weak));
-
 /* startup code */
 void __attribute__((weak,noreturn,optimize("omit-frame-pointer"))) __no_stack_protector _start(void)
 {
 	__asm__ volatile (
 		".option push\n"
 		".option norelax\n"
-		"lla   gp, __global_pointer$\n"
+		"lla  gp, __global_pointer$\n"
 		".option pop\n"
 #ifdef _NOLIBC_STACKPROTECTOR
-		"call __stack_chk_init\n"    /* initialize stack protector                          */
+		"call __stack_chk_init\n"	/* initialize stack protector			*/
 #endif
-		REG_L" a0, 0(sp)\n"          /* argc (a0) was in the stack                          */
-		"add   a1, sp, "SZREG"\n"    /* argv (a1) = sp                                      */
-		"slli  a2, a0, "PTRLOG"\n"   /* envp (a2) = SZREG*argc ...                          */
-		"add   a2, a2, "SZREG"\n"    /*             + SZREG (skip null)                     */
-		"add   a2,a2,a1\n"           /*             + argv                                  */
-
-		"add   a3, a2, zero\n"       /* iterate a3 over envp to find auxv (after NULL)      */
-		"0:\n"                       /* do {                                                */
-		REG_L" a4, 0(a3)\n"          /*   a4 = *a3;                                         */
-		"add   a3, a3, "SZREG"\n"    /*   a3 += sizeof(void*);                              */
-		"bne   a4, zero, 0b\n"       /* } while (a4);                                       */
-		"lui   a4, %hi(_auxv)\n"     /* a4 = &_auxv (high bits)                             */
-		REG_S" a3, %lo(_auxv)(a4)\n" /* store a3 into _auxv                                 */
-
-		"lui   a3, %hi(environ)\n"   /* a3 = &environ (high bits)                           */
-		REG_S" a2,%lo(environ)(a3)\n"/* store envp(a2) into environ                         */
-		"andi  sp,a1,-16\n"          /* sp must be 16-byte aligned                          */
-		"call  main\n"               /* main() returns the status code, we'll exit with it. */
-		"li a7, 93\n"                /* NR_exit == 93                                       */
-		"ecall\n"
+		"mv   a0, sp\n"			/* save stack pointer to a0, as arg1 of _start_c*/
+		"andi sp, a0, -16\n"		/* sp must be 16-byte aligned			*/
+		"call _start_c\n"		/* transfer to c runtime			*/
 	);
 	__builtin_unreachable();
 }
-- 
2.25.1