Add %m to printf & fix CI

%m is a format specifier that prints an error string for errno. The
specifier is technically only for syslog, but musl and glibc implement
it for printf itself. Parsing for a single specifier in a single
function is error prone, especially when syslog itself is variadic.

src/header/fcntl/linux.rs

@@ -17,4 +17,4 @@ pub const O_PATH: c_int = 0x20_0000;
 pub const FD_CLOEXEC: c_int = 0x8_0000;
 
 // Defined for compatibility
-pub const O_NDELAY: c_int = O_NONBLOCK;
+pub const O_NDELAY: c_int = O_NONBLOCK;

src/header/fcntl/redox.rs

@@ -26,4 +26,4 @@ pub const FD_CLOEXEC: c_int = 0x0100_0000;
 pub const O_NOCTTY: c_int = 0x00000200;
 
 // Defined for compatibility
-pub const O_NDELAY: c_int = O_NONBLOCK;
+pub const O_NDELAY: c_int = O_NONBLOCK;

src/header/stdio/printf.rs

@@ -7,7 +7,7 @@ use alloc::{
 use core::{cmp, ffi::VaList, fmt, num::FpCategory, ops::Range, slice};
 
 use crate::{
-    header::errno::EILSEQ,
+    header::errno::{self, EILSEQ},
     platform::{self, types::*},
 };
 
@@ -588,6 +588,18 @@ impl Iterator for PrintfIter {
                 b'c' => FmtKind::Char,
                 b'p' => FmtKind::Pointer,
                 b'n' => FmtKind::GetWritten,
+                b'm' => {
+                    // %m is technically for syslog only, but musl and glibc implement it for
+                    // printf because it is difficult and error prone to implement a format
+                    // specifier for just *one* function.
+                    self.format = self.format.add(1);
+                    return Some(Ok(PrintfFmt::Plain(
+                        errno::STR_ERROR
+                            .get(platform::ERRNO.get() as usize)
+                            .map(|e| e.as_bytes())
+                            .unwrap_or(b"unknown error"),
+                    )));
+                }
                 _ => return Some(Err(())),
             };
             self.format = self.format.add(1);

tests/expected/bins_dynamic/stdio/printf.stdout

@@ -67,6 +67,8 @@ printed: test string, value: 11
 printed: test string 2, value: 13
 printed: test string 2, value: 13
 
+%m: Owner died
+
 C23:
 Binary %b: 100
 Binary %b alternate: 0b100

tests/expected/bins_static/stdio/printf.stdout

@@ -67,6 +67,8 @@ printed: test string, value: 11
 printed: test string 2, value: 13
 printed: test string 2, value: 13
 
+%m: Owner died
+
 C23:
 Binary %b: 100
 Binary %b alternate: 0b100

tests/stdio/printf.c

@@ -1,3 +1,4 @@
+#include <errno.h>
 #include <stdio.h>
 #include <stdlib.h> // free()
 #include <math.h> // INFINITY, NAN constants
@@ -91,9 +92,14 @@ int main(void) {
     printf("printed: %s, value: %d\n", s, res);
     free(s);
 
+    errno = EOWNERDEAD;
+    printf("\n%%m: %m\n");
+
     puts("\nC23:");
     printf("Binary %%b: %b\n", 4);
     printf("Binary %%b alternate: %#b\n", 4);
     printf("Binary %%B: %B\n", 4);
     printf("Binary %%B alternate: %#B\n", 4);
+
+    return EXIT_SUCCESS;
 }