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Remove nonexistent SFrame flag #1899

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Remove nonexistent SFrame flag #1899

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d4670cd
accept sframe V3 only
mati865 May 6, 2026
fe83ed5
split out preamble
mati865 May 6, 2026
9b81d70
update size of `sfdi_func_start_offset`
mati865 May 6, 2026
d1766ec
Update offset for `sfdi_func_start_fre_off`
mati865 May 6, 2026
a127025
Update size of the FDE
mati865 May 6, 2026
ff0c709
Account for FDE split in SFrame V3
mati865 May 6, 2026
d0da052
Consider only hosts with SFrame V3 as supported
mati865 May 7, 2026
1b337e8
Remove nonexistent SFrame flag
mati865 May 7, 2026
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104 changes: 58 additions & 46 deletions libwild/src/sframe.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -9,15 +9,16 @@ use std::convert::TryInto;
// Magic value identifying an SFrame section.
const SFRAME_MAGIC: u16 = 0xdee2;
// Current supported SFrame version.
const SFRAME_VERSION_2: u8 = 2;
const SFRAME_VERSION_3: u8 = 3;

const FLAG_FDE_SORTED: u8 = 0x1;
const FLAG_FRAME_POINTER: u8 = 0x2;
const FLAG_FUNC_START_PCREL: u8 = 0x4;
const FLAG_AARCH64_PAUTH: u8 = 0x8;

const HEADER_SIZE: usize = 0x1c;
const FDE_SIZE: usize = 20;
const FDE_INDEX_SIZE: usize = 16;
// const FDE_ATTR_SIZE: usize = 5;
// const FDE_SIZE: usize = FDE_INDEX_SIZE + FDE_ATTR_SIZE;

// Field offsets in the SFrame header
const VERSION_FIELD: usize = 0x02;
Expand All @@ -33,9 +34,9 @@ const FDE_START_OFFSET_FIELD: usize = 0x14;
const FRE_START_OFFSET_FIELD: usize = 0x18;

struct Entry {
bytes: [u8; FDE_SIZE],
fde_index_bytes: [u8; FDE_INDEX_SIZE],
func_addr: i128,
fre_bytes: Vec<u8>,
fde_attr_and_fre_bytes: Vec<u8>,
}

#[derive(Debug, derive_more::Display)]
Expand All @@ -46,10 +47,14 @@ pub enum SframeError {
BadMagicBytes(u16),
}

struct Header {
struct Preamble {
magic: u16,
version: u8,
flags: u8,
}

struct Header {
preamble: Preamble,
abi_arch: u8,
cfa_fixed_fp_offset: i8,
cfa_fixed_ra_offset: i8,
Expand All @@ -69,14 +74,18 @@ impl Header {
}

let version = data[VERSION_FIELD];
if version != SFRAME_VERSION_2 {
if version != SFRAME_VERSION_3 {
return Err(SframeError::UnsupportedVersion(version));
}

Ok(Header {
let preamble = Preamble {
magic,
version,
flags: data[FLAGS_FIELD],
};

Ok(Header {
preamble,
abi_arch: data[ABI_ARCH_FIELD],
cfa_fixed_fp_offset: data[CFA_FIXED_FP_OFFSET_FIELD] as i8,
cfa_fixed_ra_offset: data[CFA_FIXED_RA_OFFSET_FIELD] as i8,
Expand All @@ -90,9 +99,9 @@ impl Header {
}

fn write(&self, data: &mut [u8]) {
data[0..2].copy_from_slice(&self.magic.to_le_bytes());
data[VERSION_FIELD] = self.version;
data[FLAGS_FIELD] = self.flags;
data[0..2].copy_from_slice(&self.preamble.magic.to_le_bytes());
data[VERSION_FIELD] = self.preamble.version;
data[FLAGS_FIELD] = self.preamble.flags;
data[ABI_ARCH_FIELD] = self.abi_arch;
data[CFA_FIXED_FP_OFFSET_FIELD] = self.cfa_fixed_fp_offset as u8;
data[CFA_FIXED_RA_OFFSET_FIELD] = self.cfa_fixed_ra_offset as u8;
Expand All @@ -115,12 +124,12 @@ fn read_u32(data: &[u8], offset: usize) -> u32 {
u32::from_le_bytes(data[offset..offset + 4].try_into().unwrap())
}

fn read_i32(data: &[u8], offset: usize) -> i32 {
i32::from_le_bytes(data[offset..offset + 4].try_into().unwrap())
fn read_i64(data: &[u8], offset: usize) -> i64 {
i64::from_le_bytes(data[offset..offset + 8].try_into().unwrap())
}

fn write_i32(data: &mut [u8], offset: usize, value: i32) {
data[offset..offset + 4].copy_from_slice(&value.to_le_bytes());
fn write_i64(data: &mut [u8], offset: usize, value: i64) {
data[offset..offset + 8].copy_from_slice(&value.to_le_bytes());
}

/// Sort the SFrame FDE array in-place by the functions' start addresses.
Expand Down Expand Up @@ -166,23 +175,20 @@ pub(crate) fn sort_sframe_section(
Err(e) => bail!("Failed to parse SFrame header at offset {}: {}", offset, e),
};

let pc_rel = header.flags & FLAG_FUNC_START_PCREL != 0;
let pc_rel = header.preamble.flags & FLAG_FUNC_START_PCREL != 0;
let aux_len = header.aux_len as usize;

if first_section {
output_flags = header.flags;
output_flags = header.preamble.flags;
output_abi_arch = header.abi_arch;
output_cfa_fixed_fp_offset = header.cfa_fixed_fp_offset;
output_cfa_fixed_ra_offset = header.cfa_fixed_ra_offset;
output_aux_len = aux_len;
first_section = false;
} else {
if (header.flags & FLAG_FRAME_POINTER) == 0 {
if (header.preamble.flags & FLAG_FRAME_POINTER) == 0 {
output_flags &= !FLAG_FRAME_POINTER;
}
if (header.flags & FLAG_AARCH64_PAUTH) != 0 {
output_flags |= FLAG_AARCH64_PAUTH;
}
}

total_num_fres += header.num_fres as usize;
Expand All @@ -195,20 +201,20 @@ pub(crate) fn sort_sframe_section(
let fre_start = offset + header_end_offset + header.fre_start_offset as usize;

let num_fdes = header.num_fdes as usize;
let total_fde_bytes = FDE_SIZE
let total_fde_index_bytes = FDE_INDEX_SIZE
.checked_mul(num_fdes)
.context("SFrame FDE array size overflow")?;

let fde_end = fde_start + total_fde_bytes;
let fde_end = fde_start + total_fde_index_bytes;

if fde_end > offset + len {
bail!("SFrame FDE array truncated");
}

let mut fre_offsets = Vec::with_capacity(num_fdes + 1);
for i in 0..num_fdes {
let offset_in_section = fde_start + i * FDE_SIZE;
let fre_offset = read_u32(section, offset_in_section + 8);
let offset_in_section = fde_start + i * FDE_INDEX_SIZE;
let fre_offset = read_u32(section, offset_in_section + 12);
fre_offsets.push(fre_offset);
}

Expand All @@ -222,18 +228,19 @@ pub(crate) fn sort_sframe_section(
fre_offsets.dedup();

for index in 0..num_fdes {
let offset_in_section = fde_start + index * FDE_SIZE;
let mut bytes = [0u8; FDE_SIZE];
bytes.copy_from_slice(&section[offset_in_section..offset_in_section + FDE_SIZE]);
let offset_in_section = fde_start + index * FDE_INDEX_SIZE;
let mut fde_index_bytes = [0u8; FDE_INDEX_SIZE];
fde_index_bytes
.copy_from_slice(&section[offset_in_section..offset_in_section + FDE_INDEX_SIZE]);

let start_value = i128::from(read_i32(&bytes, 0));
let start_value = i128::from(read_i64(&fde_index_bytes, 0));
let func_addr = if pc_rel {
section_base + (offset_in_section as i128) + start_value
} else {
section_base + start_value
};

let curr_fre_offset = read_u32(&bytes, 8);
let curr_fre_offset = read_u32(&fde_index_bytes, 12);

// Find the length of the FRE data for this function.
// It extends from curr_fre_offset to the next offset in our sorted list.
Expand All @@ -252,13 +259,13 @@ pub(crate) fn sort_sframe_section(
bail!("SFrame FRE data truncated");
}

let fre_bytes =
let fde_attr_and_fre_bytes =
section[curr_fre_abs_start..curr_fre_abs_start + curr_fre_len].to_owned();

entries.push(Entry {
bytes,
fde_index_bytes,
func_addr,
fre_bytes,
fde_attr_and_fre_bytes,
});
}
}
Expand All @@ -273,20 +280,24 @@ pub(crate) fn sort_sframe_section(
let header_end_offset = HEADER_SIZE + output_aux_len;

let fde_offset = 0;
let fde_size = num_fdes * FDE_SIZE;
let fde_size = num_fdes * FDE_INDEX_SIZE;
let fre_offset = fde_size;

let total_fre_size: usize = entries.iter().map(|e| e.fre_bytes.len()).sum();
let total_fre_size: usize = entries.iter().map(|e| e.fde_attr_and_fre_bytes.len()).sum();
let total_size = header_end_offset + fde_size + total_fre_size;

if total_size > section.len() {
bail!("Merged SFrame section too large");
}

let header = Header {
let preamble = Preamble {
magic: SFRAME_MAGIC,
version: SFRAME_VERSION_2,
version: SFRAME_VERSION_3,
flags: output_flags | FLAG_FDE_SORTED,
};

let header = Header {
preamble,
abi_arch: output_abi_arch,
cfa_fixed_fp_offset: output_cfa_fixed_fp_offset,
cfa_fixed_ra_offset: output_cfa_fixed_ra_offset,
Expand All @@ -304,27 +315,28 @@ pub(crate) fn sort_sframe_section(
let fre_start_idx = header_end_offset + fre_offset;

for (index, entry) in entries.iter().enumerate() {
let mut fde_bytes = entry.bytes;
let mut fde_bytes = entry.fde_index_bytes;

let fde_pos_in_section = fde_start_idx + index * FDE_SIZE;
let pc_rel = header.flags & FLAG_FUNC_START_PCREL != 0;
let fde_pos_in_section = fde_start_idx + index * FDE_INDEX_SIZE;
let pc_rel = header.preamble.flags & FLAG_FUNC_START_PCREL != 0;

let new_value = if pc_rel {
entry.func_addr - (section_base + fde_pos_in_section as i128)
} else {
entry.func_addr - section_base
};
let new_value_i32 = i32::try_from(new_value)
let new_value_i64 = i64::try_from(new_value)
.context("Function start address out of 32-bit range for SFrame entry")?;
write_i32(&mut fde_bytes, 0, new_value_i32);
write_i64(&mut fde_bytes, 0, new_value_i64);

fde_bytes[8..12].copy_from_slice(&(current_fre_rel_offset as u32).to_le_bytes());
fde_bytes[12..16].copy_from_slice(&(current_fre_rel_offset as u32).to_le_bytes());

section[fde_pos_in_section..fde_pos_in_section + FDE_SIZE].copy_from_slice(&fde_bytes);
section[fde_pos_in_section..fde_pos_in_section + FDE_INDEX_SIZE]
.copy_from_slice(&fde_bytes);

let fre_len = entry.fre_bytes.len();
let fre_len = entry.fde_attr_and_fre_bytes.len();
let fre_pos = fre_start_idx + current_fre_rel_offset;
section[fre_pos..fre_pos + fre_len].copy_from_slice(&entry.fre_bytes);
section[fre_pos..fre_pos + fre_len].copy_from_slice(&entry.fde_attr_and_fre_bytes);

current_fre_rel_offset += fre_len;
}
Expand Down
2 changes: 1 addition & 1 deletion wild/tests/integration_tests.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -937,7 +937,7 @@ int main(void) {
.arg("-c")
.arg("-O0")
.arg("-fomit-frame-pointer")
.arg("-Wa,--gsframe")
.arg("-Wa,--gsframe-3")
.arg(&source_path)
.arg("-o")
.arg(&obj_path);
Expand Down
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