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    Subject[PATCH 5.4 012/320] tools/nolibc: fix incorrect truncation of exit code
    Date
    From: Willy Tarreau <w@1wt.eu>

    commit de0244ae40ae91145faaf164a4252347607c3711 upstream.

    Ammar Faizi reported that our exit code handling is wrong. We truncate
    it to the lowest 8 bits but the syscall itself is expected to take a
    regular 32-bit signed integer, not an unsigned char. It's the kernel
    that later truncates it to the lowest 8 bits. The difference is visible
    in strace, where the program below used to show exit(255) instead of
    exit(-1):

    int main(void)
    {
    return -1;
    }

    This patch applies the fix to all archs. x86_64, i386, arm64, armv7 and
    mips were all tested and confirmed to work fine now. Risc-v was not
    tested but the change is trivial and exactly the same as for other archs.

    Reported-by: Ammar Faizi <ammar.faizi@students.amikom.ac.id>
    Cc: stable@vger.kernel.org
    Signed-off-by: Willy Tarreau <w@1wt.eu>
    Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    tools/include/nolibc/nolibc.h | 13 +++++--------
    1 file changed, 5 insertions(+), 8 deletions(-)

    --- a/tools/include/nolibc/nolibc.h
    +++ b/tools/include/nolibc/nolibc.h
    @@ -437,7 +437,7 @@ asm(".section .text\n"
    "xor %ebp, %ebp\n" // zero the stack frame
    "and $-16, %rsp\n" // x86 ABI : esp must be 16-byte aligned before call
    "call main\n" // main() returns the status code, we'll exit with it.
    - "movzb %al, %rdi\n" // retrieve exit code from 8 lower bits
    + "mov %eax, %edi\n" // retrieve exit code (32 bit)
    "mov $60, %rax\n" // NR_exit == 60
    "syscall\n" // really exit
    "hlt\n" // ensure it does not return
    @@ -625,9 +625,9 @@ asm(".section .text\n"
    "push %ebx\n" // support both regparm and plain stack modes
    "push %eax\n"
    "call main\n" // main() returns the status code in %eax
    - "movzbl %al, %ebx\n" // retrieve exit code from lower 8 bits
    - "movl $1, %eax\n" // NR_exit == 1
    - "int $0x80\n" // exit now
    + "mov %eax, %ebx\n" // retrieve exit code (32-bit int)
    + "movl $1, %eax\n" // NR_exit == 1
    + "int $0x80\n" // exit now
    "hlt\n" // ensure it does not
    "");

    @@ -811,7 +811,6 @@ asm(".section .text\n"
    "and %r3, %r1, $-8\n" // AAPCS : sp must be 8-byte aligned in the
    "mov %sp, %r3\n" // callee, an bl doesn't push (lr=pc)
    "bl main\n" // main() returns the status code, we'll exit with it.
    - "and %r0, %r0, $0xff\n" // limit exit code to 8 bits
    "movs r7, $1\n" // NR_exit == 1
    "svc $0x00\n"
    "");
    @@ -1008,7 +1007,6 @@ asm(".section .text\n"
    "add x2, x2, x1\n" // + argv
    "and sp, x1, -16\n" // sp must be 16-byte aligned in the callee
    "bl main\n" // main() returns the status code, we'll exit with it.
    - "and x0, x0, 0xff\n" // limit exit code to 8 bits
    "mov x8, 93\n" // NR_exit == 93
    "svc #0\n"
    "");
    @@ -1213,7 +1211,7 @@ asm(".section .text\n"
    "addiu $sp,$sp,-16\n" // the callee expects to save a0..a3 there!
    "jal main\n" // main() returns the status code, we'll exit with it.
    "nop\n" // delayed slot
    - "and $a0, $v0, 0xff\n" // limit exit code to 8 bits
    + "move $a0, $v0\n" // retrieve 32-bit exit code from v0
    "li $v0, 4001\n" // NR_exit == 4001
    "syscall\n"
    ".end __start\n"
    @@ -1411,7 +1409,6 @@ asm(".section .text\n"
    "add a2,a2,a1\n" // + argv
    "andi sp,a1,-16\n" // sp must be 16-byte aligned
    "call main\n" // main() returns the status code, we'll exit with it.
    - "andi a0, a0, 0xff\n" // limit exit code to 8 bits
    "li a7, 93\n" // NR_exit == 93
    "ecall\n"
    "");

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