Newlib-1.11.0 Bug

[Marcio Rogério Juliato]

Dear Sirs,
I found a bug in the file newlib-1.11.0/newlib/libc/machine/mips/strlen.c
when using newlib to compile programs to the R3000 processor (a 32-bits
MIPS 1 processor supported by newlib).
The "lbu $3,0($4)" instruction loads a value into the register $3, which
is going to be used by the next instruction "bnez $3,1b". But notice that
the R3000 does not have pipeline stall, i.e. there is no time enough to
load a correct value into the $3 register before its use. It means that
the instruction "bnez $3,1b" gets the wrong value to the comparison.
The problematic source code is shown below.

...

#else
__asm__(""                      /* 32-bit MIPS targets */
        "       .set    noreorder\n"
        "       .set    nomacro\n"
        "       .globl  strlen\n"
        "       .ent    strlen\n"
        "strlen:\n"
        "       addiu   $2,$4,1\n"
        "\n"
        "1:     lbu     $3,0($4)\n"
        "       bnez    $3,1b\n"     /* <================ PROBLEM with the
$3 value!!!!!! */
        "       addiu   $4,$4,1\n"
        "\n"
        "       jr      $31\n"
        "       subu    $2,$4,$2\n"
        "       .end    strlen\n"
        "       .set    macro\n"
        "       .set    reorder\n");
#endif


THE PATCH:
A simplier correction to this problem could be the insertion of a NOP
instruction among the other two. We could also insert another instruction
instead od NOP, but we should take care with data dependency.
Below is shown the simplier aproach.

...

#else
__asm__(""                      /* 32-bit MIPS targets */
        "       .set    noreorder\n"
        "       .set    nomacro\n"
        "       .globl  strlen\n"
        "       .ent    strlen\n"
        "strlen:\n"
        "       addiu   $2,$4,1\n"
        "\n"
        "1:     lbu     $3,0($4)\n"
        "       nop\n"               /* <======= NOP INSERTION */
        "       bnez    $3,1b\n"
        "       addiu   $4,$4,1\n"
        "\n"
        "       jr      $31\n"
        "       subu    $2,$4,$2\n"
        "       .end    strlen\n"
        "       .set    macro\n"
        "       .set    reorder\n");
#endif


I would like to know if there is a standard bug submission that I should
follow...

Best regards,
Marcio Juliato