From 1a8eee6d2a1d79412902331b74283eec77414c6b Mon Sep 17 00:00:00 2001
From: Pierre-Hugues Husson <phh@phh.me>
Date: Sat, 19 Feb 2022 08:20:25 -0500
Subject: [PATCH 1/2] Add new mechanism to fake vendor props on a per-process
 basis

This reads debug.phh.props.<process name>. If its value is "vendor",
then ro.product.device/ro.product.manufacturer is read from vendor
---
 libc/system_properties/system_properties.cpp | 38 ++++++++++++++++++++
 1 file changed, 38 insertions(+)

diff --git a/libc/system_properties/system_properties.cpp b/libc/system_properties/system_properties.cpp
index 1cb15c3df..d6e7e3e68 100644
--- a/libc/system_properties/system_properties.cpp
+++ b/libc/system_properties/system_properties.cpp
@@ -35,6 +35,7 @@
 #include <sys/stat.h>
 #include <sys/types.h>
 #include <unistd.h>
+#include <fcntl.h>
 
 #include <new>
 
@@ -50,6 +51,32 @@
 #define SERIAL_DIRTY(serial) ((serial)&1)
 #define SERIAL_VALUE_LEN(serial) ((serial) >> 24)
 
+static char comm[128];
+static bool self_ok = false;
+static char comm_override[PROP_VALUE_MAX];
+
+static void read_self() {
+  //NB: Not atomic, but should be good enough, there is no possible corruption from concurrency
+  if(self_ok) return;
+  self_ok = true;
+
+  int fd = open("/proc/self/comm", O_RDONLY);
+  if(fd<0) return;
+  read(fd, comm, sizeof(comm)-1);
+  for(unsigned i=0; i<sizeof(comm); i++)
+    if(comm[i] == '\n')
+      comm[i] = 0;
+  close(fd);
+
+  //That's calling ourselves but that's fine because we already have self_ok = true
+  char propName[PROP_NAME_MAX];
+  memset(propName, 0, PROP_NAME_MAX);
+  strncpy(propName, "debug.phh.props.", PROP_NAME_MAX - 1);
+  strncat(propName, comm, PROP_NAME_MAX - 1);
+
+  __system_property_get(propName, comm_override);
+}
+
 static bool is_dir(const char* pathname) {
   struct stat info;
   if (stat(pathname, &info) == -1) {
@@ -216,6 +243,17 @@ void SystemProperties::ReadCallback(const prop_info* pi,
 }
 
 int SystemProperties::Get(const char* name, char* value) {
+  read_self();
+  if(strcmp(comm_override, "vendor") == 0) {
+    if(strcmp(name, "ro.product.device") == 0) {
+      int r = Get("ro.product.vendor.device", value);
+      if(r>0) return r;
+    }
+    if(strcmp(name, "ro.product.manufacturer") == 0) {
+      int r = Get("ro.product.vendor.manufacturer", value);
+      if(r>0) return r;
+    }
+  }
   const prop_info* pi = Find(name);
 
   if (pi != nullptr) {
-- 
2.34.1