From c317de7f45b07b5149bb9bd413d6ee5a851c9dc8 Mon Sep 17 00:00:00 2001
From: Andrew Gallagher <andrewjcg@meta.com>
Date: Wed, 25 Oct 2023 19:55:23 -0700
Subject: [PATCH] Align virtual address base

This fixes a bug where we were calculating incorrect address offsets.
---
 Cargo.lock           | 11 +++++++++++
 Cargo.toml           |  1 +
 src/binary_parser.rs |  8 +++++---
 3 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/Cargo.lock b/Cargo.lock
index 3fdf60cf..0664710e 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -953,6 +953,16 @@ version = "6.6.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "e2355d85b9a3786f481747ced0e0ff2ba35213a1f9bd406ed906554d7af805a1"
 
+[[package]]
+name = "page_size"
+version = "0.6.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "30d5b2194ed13191c1999ae0704b7839fb18384fa22e49b57eeaa97d79ce40da"
+dependencies = [
+ "libc",
+ "winapi",
+]
+
 [[package]]
 name = "parking_lot_core"
 version = "0.9.10"
@@ -1065,6 +1075,7 @@ dependencies = [
  "lru",
  "memmap2",
  "num-traits",
+ "page_size",
  "proc-maps",
  "py-spy-testdata",
  "rand",
diff --git a/Cargo.toml b/Cargo.toml
index c0e6c946..8327bd32 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -31,6 +31,7 @@ lru = "0.10"
 num-traits = "0.2"
 regex = ">=1.6.0"
 tempfile = "3.6.0"
+page_size = "0.6.0"
 proc-maps = "0.4.0"
 memmap2 = "0.9.4"
 cpp_demangle = "0.4"
diff --git a/src/binary_parser.rs b/src/binary_parser.rs
index 4df02687..7dae27b9 100644
--- a/src/binary_parser.rs
+++ b/src/binary_parser.rs
@@ -150,9 +150,11 @@ pub fn parse_binary(filename: &Path, addr: u64, size: u64) -> Result<BinaryInfo,
                     )
                 })?;
 
-            // p_vaddr may be larger than the map address in case when the header has an offset and
-            // the map address is relatively small. In this case we can default to 0.
-            let offset = offset.saturating_sub(program_header.p_vaddr);
+            // Align the virtual address offset, then subtract it from the offset
+            // to get real offset for symbol addresses in the file.
+            let aligned_vaddr =
+                program_header.p_vaddr - (program_header.p_vaddr % page_size::get() as u64);
+            let offset = offset - aligned_vaddr;
 
             let mut bss_addr = 0;
             let mut bss_size = 0;