From a3905888895a919bf6a8922b65289a8428823b17 Mon Sep 17 00:00:00 2001
From: Daniel Trugman <dtrugman@gmail.com>
Date: Thu, 16 May 2024 10:48:43 +0100
Subject: [PATCH] Allow compilation of 32-bit on 64-bit machines

---
 CMakeLists.txt             | 6 ++++++
 README.md                  | 2 ++
 docker/Dockerfile-debian12 | 2 +-
 src/mem.cpp                | 2 +-
 4 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 294ea22..dbb29e3 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -22,6 +22,7 @@ endif ()
 # Flags that are NOT expected to be shared when added as sub-directory
 # ------------------------------------------------------------------------
 
+option (pfs_BUILD_32BIT "Build a 32-bit executable" OFF)
 option (pfs_BUILD_COVERAGE "Enable coverage instrumentation" OFF)
 option (pfs_BUILD_ASAN "Enable address sanitizer" OFF)
 option (pfs_BUILD_SAMPLES "Build samples" ON)
@@ -49,6 +50,11 @@ target_include_directories(
     $<INSTALL_INTERFACE:include>
 )
 
+if (pfs_BUILD_32BIT)
+    set (pfs_BUILD_32BIT_FLAGS -m32)
+    target_compile_options (pfs PUBLIC ${pfs_BUILD_32BIT_FLAGS})
+endif ()
+
 if (pfs_BUILD_COVERAGE)
     set (pfs_BUILD_COVERAGE_FLAGS -O0 --coverage)
     target_compile_options (pfs PUBLIC ${pfs_BUILD_COVERAGE_FLAGS})
diff --git a/README.md b/README.md
index a20fbfd..be268ea 100644
--- a/README.md
+++ b/README.md
@@ -14,6 +14,8 @@ Run `cmake . && make`
 ### Currently supported CMake configuration flags:
 
 - `CMAKE_BUILD_TYPE=<Debug|Release>`: Standard CMake flags to control build type (DEFAULT: Debug)
+- `pfs_BUILD_32BIT=<ON|OFF>`: ON to compile a 32-bit binary. OFF to compile using the default configuration of your compiler (DEFAULT: `OFF`))
+  - You will need the `g++-multilib` package.
 - `pfs_BUILD_SHARED_LIBS=<ON|OFF>`: ON to compile a shared library. OFF to compile a static library (DEFAULT: Inherit `BUILD_SHARE_LIBS`, which is `OFF` by default))
 - `pfs_BUILD_ASAN=<ON|OFF>`: ON to enable address sanitizer (DEFAULT: `OFF`)
 - `pfs_BUILD_SAMPLES=<ON|OFF>`: ON to build the sample programs (DEFAULT: `ON`)
diff --git a/docker/Dockerfile-debian12 b/docker/Dockerfile-debian12
index 86b5eb6..a6a3743 100644
--- a/docker/Dockerfile-debian12
+++ b/docker/Dockerfile-debian12
@@ -1,4 +1,4 @@
-FROM debian:bookworm
+FROM i386/debian:bookworm
 
 WORKDIR /pfs
 
diff --git a/src/mem.cpp b/src/mem.cpp
index 48a833f..da649f5 100644
--- a/src/mem.cpp
+++ b/src/mem.cpp
@@ -51,7 +51,7 @@ std::vector<uint8_t> mem::read(loff_t offset, size_t bytes)
 
     struct iovec iov = {&buffer[0], buffer.size()};
 
-    ssize_t bytes_read = preadv64(_fd, &iov, 1, offset);
+    ssize_t bytes_read = preadv(_fd, &iov, 1, offset);
     if (bytes_read == -1)
     {
         throw std::system_error(errno, std::system_category(),