From: Patrick Steinhardt Date: Mon, 08 Sep 2025 14:13:12 GMT Subject: [PATCH RFC v3 5/8] rust: implement a test balloon via the "varint" subsystem Message-ID: <20250908-b4-pks-rust-breaking-change-v3-5-1cd7189fed3b@pks.im> In-Reply-To: <20250908-b4-pks-rust-breaking-change-v3-0-1cd7189fed3b@pks.im> Implement a trivial test balloon for our Rust build infrastructure by reimplementing the "varint.c" subsystem in Rust. This subsystem is chosen because it is trivial to convert and because it doesn't have any dependencies to other components of Git. If support for Rust is enabled, we stop compiling "varint.c" and instead compile and use "src/varint.rs". Signed-off-by: Patrick Steinhardt --- Makefile | 3 ++ meson.build | 5 ++- src/lib.rs | 1 + src/meson.build | 1 + src/varint.rs | 95 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 5 files changed, 104 insertions(+), 1 deletion(-) diff --git a/Makefile b/Makefile index 94950a0ffe2..7640d0d76ac 100644 --- a/Makefile +++ b/Makefile @@ -1307,7 +1307,9 @@ LIB_OBJS += urlmatch.o LIB_OBJS += usage.o LIB_OBJS += userdiff.o LIB_OBJS += utf8.o +ifndef WITH_RUST LIB_OBJS += varint.o +endif LIB_OBJS += version.o LIB_OBJS += versioncmp.o LIB_OBJS += walker.o @@ -1499,6 +1501,7 @@ CLAR_TEST_OBJS += $(UNIT_TEST_DIR)/unit-test.o UNIT_TEST_OBJS += $(UNIT_TEST_DIR)/test-lib.o RUST_SOURCES += src/lib.rs +RUST_SOURCES += src/varint.rs GIT-VERSION-FILE: FORCE @OLD=$$(cat $@ 2>/dev/null || :) && \ diff --git a/meson.build b/meson.build index 3d6601225ba..48b80cb832c 100644 --- a/meson.build +++ b/meson.build @@ -522,7 +522,6 @@ libgit_sources = [ 'usage.c', 'userdiff.c', 'utf8.c', - 'varint.c', 'version.c', 'versioncmp.c', 'walker.c', @@ -1716,6 +1715,10 @@ rust_option = get_option('rust').disable_auto_if(not rust_available) if rust_option.allowed() subdir('src') libgit_c_args += '-DWITH_RUST' +else + libgit_sources += [ + 'varint.c', + ] endif libgit = declare_dependency( diff --git a/src/lib.rs b/src/lib.rs index e69de29bb2d..9da70d8b57d 100644 --- a/src/lib.rs +++ b/src/lib.rs @@ -0,0 +1 @@ +pub mod varint; diff --git a/src/meson.build b/src/meson.build index 59e810b4d41..03b71a5c7bd 100644 --- a/src/meson.build +++ b/src/meson.build @@ -1,5 +1,6 @@ libgit_rs_sources = [ 'lib.rs', + 'varint.rs', ] if meson.version().version_compare('>=1.5.0') diff --git a/src/varint.rs b/src/varint.rs new file mode 100644 index 00000000000..7e50cfa09fe --- /dev/null +++ b/src/varint.rs @@ -0,0 +1,95 @@ +use std::os::raw::c_int; +use std::os::raw::c_uchar; + +#[no_mangle] +pub unsafe extern "C" fn decode_varint(bufp: *mut *const c_uchar) -> usize { + let mut buf = *bufp; + let mut c = *buf; + let mut val = usize::from(c & 127); + + buf = buf.add(1); + + while (c & 128) != 0 { + val = val.wrapping_add(1); + if val == 0 || val.leading_zeros() < 7 { + return 0; // overflow + } + + c = *buf; + buf = buf.add(1); + + val = (val << 7) + usize::from(c & 127); + } + + *bufp = buf; + val +} + +#[no_mangle] +pub unsafe extern "C" fn encode_varint(value: usize, buf: *mut c_uchar) -> c_int { + let mut varint: [u8; 16] = [0; 16]; + let mut pos = varint.len() - 1; + + varint[pos] = (value & 127) as u8; + + let mut value = value >> 7; + while value != 0 { + pos -= 1; + value -= 1; + varint[pos] = 128 | (value & 127) as u8; + value >>= 7; + } + + if !buf.is_null() { + std::ptr::copy_nonoverlapping(varint.as_ptr().add(pos), buf, varint.len() - pos); + } + + (varint.len() - pos) as c_int +} + +#[cfg(test)] +mod tests { + use super::*; + + #[test] + fn test_decode_varint() { + unsafe { + assert_eq!(decode_varint(&mut [0x00].as_slice().as_ptr()), 0); + assert_eq!(decode_varint(&mut [0x01].as_slice().as_ptr()), 1); + assert_eq!(decode_varint(&mut [0x7f].as_slice().as_ptr()), 127); + assert_eq!(decode_varint(&mut [0x80, 0x00].as_slice().as_ptr()), 128); + assert_eq!(decode_varint(&mut [0x80, 0x01].as_slice().as_ptr()), 129); + assert_eq!(decode_varint(&mut [0x80, 0x7f].as_slice().as_ptr()), 255); + + // Overflows are expected to return 0. + assert_eq!(decode_varint(&mut [0x88; 16].as_slice().as_ptr()), 0); + } + } + + #[test] + fn test_encode_varint() { + unsafe { + let mut varint: [u8; 16] = [0; 16]; + + assert_eq!(encode_varint(0, std::ptr::null_mut()), 1); + + assert_eq!(encode_varint(0, varint.as_mut_slice().as_mut_ptr()), 1); + assert_eq!(varint, [0; 16]); + + assert_eq!(encode_varint(10, varint.as_mut_slice().as_mut_ptr()), 1); + assert_eq!(varint, [10, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]); + + assert_eq!(encode_varint(127, varint.as_mut_slice().as_mut_ptr()), 1); + assert_eq!(varint, [127, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]); + + assert_eq!(encode_varint(128, varint.as_mut_slice().as_mut_ptr()), 2); + assert_eq!(varint, [128, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]); + + assert_eq!(encode_varint(129, varint.as_mut_slice().as_mut_ptr()), 2); + assert_eq!(varint, [128, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]); + + assert_eq!(encode_varint(255, varint.as_mut_slice().as_mut_ptr()), 2); + assert_eq!(varint, [128, 127, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]); + } + } +} -- 2.51.0.417.g1ba7204a04.dirty