1 files changed, 36 insertions, 25 deletions
diff --git a/README.md b/README.md
index 3990731..95cb5f8 100644
--- a/README.md
+++ b/README.md
@@ -32,7 +32,7 @@ bitbake-layers add-layer ../meta-clang
 Check `conf/bblayers.conf` to see that meta-clang is added to layer mix e.g.
-# Default Compiler Switch
+# Default Compiler
 Note that by default gcc will remain the system compiler, however if you wish
 clang to be the default compiler then set
@@ -47,45 +47,56 @@ you can select clang per recipe too by writing bbappends for them containing
 ```shell
 TOOLCHAIN = "clang"
 ```
+also look at `conf/nonclangable.conf` for list of recipes which do not yet fully
+build with clang
-# Default C++ Standard Library Switch
+# Default Compiler Runtime
-Note that by default clang libc++ is default C++ standard library, however if you wish
+Default is to use GNU runtime `RUNTIME = "gnu"` which consists of libgcc, libstdc++ to provide C/C++
-to keep GNU libstdc++ to be the default then set
+runtime support. However its possible to use LLVM runtime to replace it where
+compile-rt, llvm libunwind, and libc++ are used to provide C/C++ runtime, while
+GNU runtime works with both GCC and Clang, LLVM runtime is only tested with Clang
+compiler, Switching to use LLVM runtime is done via a config metadata knob
 ```shell
-LIBCPLUSPLUS = ""
+RUNTIME = "llvm"
 ```
-in `local.conf`.
+RUNTIME variable influences individual runtime elements and can be set explcitly as well
-You can select libstdc++ per package too by writing bbappends for them containing
+e.g. `LIBCPLUSPLUS` `COMPILER_RT` and `UNWINDLIB`
-```shell
+Please note that this will still use crt files from GNU compiler always, while llvm now
-LIBCPLUSPLUS_toolchain-clang_pn-<recipe> = ""
+do provide crt files, they have not been yet intergrated into toolchain
-```
-# Default Compiler Runtime ( Compiler-rt + libc++ )
+# Default C++ Standard Library Switch
-By default, clang build from meta-clang uses clang runtime ( compiler-rt + libc++ + libunwind ) out of box
+Using RUNTIME bariable will select which C++ runtime is used, however it can be overridden
-However, it is possible to switch to using gcc runtime as default, In order to do that
+if needed to by modifying `LIBCPLUSPLUS` variable, usually defaults used by `RUNTIME` is
-following settings are needed in site configurations e.g. in `local.conf`
+best fit. e.g. below we select LLVM C++ as default C++ runtime.
 ```shell
-TOOLCHAIN ?= "clang"
+LIBCPLUSPLUS = "--stdlib=libc++"
-LIBCPLUSPLUS = ""
+```
-COMPILER_RT = ""
-UNWINDLIB = ""
+in `local.conf`.
+You can select libstdc++ per package too by writing bbappends for them containing
+```shell
+LIBCPLUSPLUS_toolchain-clang_pn-<recipe> = "--stdlibc=libc++"
 ```
+Defaults are chosen to be GNU for maximum compatibility with existing GNU systems. Its always
+good to use single runtime on a system, mixing runtimes can cause complications during
+compilation as well as runtime. However, its upto distribution policies to decide which runtime
+to use.
-# Removing clang from generated SDK toolchain
+# Adding clang in generated SDK toolchain
-clang based cross compiler is automatically included into the generated SDK using `bitbake meta-toolchain` or
+clang based cross compiler is not included into the generated SDK using `bitbake meta-toolchain` or
-`bitbake -cpopulate_sdk <image>` in circumstanced where clang is not expected to be part of SDK, then reset `CLANGSDK`
+`bitbake -cpopulate_sdk <image>` if clang is expected to be part of SDK, add `CLANGSDK = "1"`
-variable in `local.conf`
+in `local.conf`
 ```shell
-CLANGSDK = ""
+CLANGSDK = "1"
 ```
 # Building
@@ -104,7 +115,7 @@ $ runqemu nographic
 # Limitations
 Few components do not build with clang, if you have a component to add to that list
-simply add it to conf/nonclangable.inc e.g.
+simply add it to `conf/nonclangable.inc` e.g.
 ```shell
 TOOLCHAIN_pn-<recipe> = "gcc"
@@ -112,7 +123,7 @@ TOOLCHAIN_pn-<recipe> = "gcc"
 and OE will start using gcc to cross compile that recipe.
-And if a component does not build with libc++, you can add it to `conf/nonclangable.inc` e.g.
+if a component does not build with libc++, you can add it to `conf/nonclangable.inc` e.g.
 ```shell
 CXX_remove_pn-<recipe>_toolchain-clang = " -stdlib=libc++ "

diff --git a/README.md b/README.md index 3990731..95cb5f8 100644 --- a/README.md +++ b/README.md
@@ -32,7 +32,7 @@ bitbake-layers add-layer ../meta-clang
32		32
33	Check `conf/bblayers.conf` to see that meta-clang is added to layer mix e.g.	33	Check `conf/bblayers.conf` to see that meta-clang is added to layer mix e.g.
34		34
35	# Default Compiler Switch	35	# Default Compiler
36		36
37	Note that by default gcc will remain the system compiler, however if you wish	37	Note that by default gcc will remain the system compiler, however if you wish
38	clang to be the default compiler then set	38	clang to be the default compiler then set
@@ -47,45 +47,56 @@ you can select clang per recipe too by writing bbappends for them containing
47	```shell	47	```shell
48	TOOLCHAIN = "clang"	48	TOOLCHAIN = "clang"
49	```	49	```
		50	also look at `conf/nonclangable.conf` for list of recipes which do not yet fully
		51	build with clang
50		52
51	# Default C++ Standard Library Switch	53	# Default Compiler Runtime
52		54
53	Note that by default clang libc++ is default C++ standard library, however if you wish	55	Default is to use GNU runtime `RUNTIME = "gnu"` which consists of libgcc, libstdc++ to provide C/C++
54	to keep GNU libstdc++ to be the default then set	56	runtime support. However its possible to use LLVM runtime to replace it where
		57	compile-rt, llvm libunwind, and libc++ are used to provide C/C++ runtime, while
		58	GNU runtime works with both GCC and Clang, LLVM runtime is only tested with Clang
		59	compiler, Switching to use LLVM runtime is done via a config metadata knob
55		60
56	```shell	61	```shell
57	LIBCPLUSPLUS = ""	62	RUNTIME = "llvm"
58	```	63	```
59		64
60	in `local.conf`.	65	RUNTIME variable influences individual runtime elements and can be set explcitly as well
61	You can select libstdc++ per package too by writing bbappends for them containing	66	e.g. `LIBCPLUSPLUS` `COMPILER_RT` and `UNWINDLIB`
62		67
63	```shell	68	Please note that this will still use crt files from GNU compiler always, while llvm now
64	LIBCPLUSPLUS_toolchain-clang_pn-<recipe> = ""	69	do provide crt files, they have not been yet intergrated into toolchain
65	```
66		70
67	# Default Compiler Runtime ( Compiler-rt + libc++ )	71	# Default C++ Standard Library Switch
68		72
69	By default, clang build from meta-clang uses clang runtime ( compiler-rt + libc++ + libunwind ) out of box	73	Using RUNTIME bariable will select which C++ runtime is used, however it can be overridden
70	However, it is possible to switch to using gcc runtime as default, In order to do that	74	if needed to by modifying `LIBCPLUSPLUS` variable, usually defaults used by `RUNTIME` is
71	following settings are needed in site configurations e.g. in `local.conf`	75	best fit. e.g. below we select LLVM C++ as default C++ runtime.
72		76
73	```shell	77	```shell
74	TOOLCHAIN ?= "clang"	78	LIBCPLUSPLUS = "--stdlib=libc++"
75	LIBCPLUSPLUS = ""	79	```
76	COMPILER_RT = ""	80
77	UNWINDLIB = ""	81	in `local.conf`.
		82	You can select libstdc++ per package too by writing bbappends for them containing
78		83
		84	```shell
		85	LIBCPLUSPLUS_toolchain-clang_pn-<recipe> = "--stdlibc=libc++"
79	```	86	```
		87	Defaults are chosen to be GNU for maximum compatibility with existing GNU systems. Its always
		88	good to use single runtime on a system, mixing runtimes can cause complications during
		89	compilation as well as runtime. However, its upto distribution policies to decide which runtime
		90	to use.
80		91
81	# Removing clang from generated SDK toolchain	92	# Adding clang in generated SDK toolchain
82		93
83	clang based cross compiler is automatically included into the generated SDK using `bitbake meta-toolchain` or	94	clang based cross compiler is not included into the generated SDK using `bitbake meta-toolchain` or
84	`bitbake -cpopulate_sdk <image>` in circumstanced where clang is not expected to be part of SDK, then reset `CLANGSDK`	95	`bitbake -cpopulate_sdk <image>` if clang is expected to be part of SDK, add `CLANGSDK = "1"`
85	variable in `local.conf`	96	in `local.conf`
86		97
87	```shell	98	```shell
88	CLANGSDK = ""	99	CLANGSDK = "1"
89	```	100	```
90		101
91	# Building	102	# Building
@@ -104,7 +115,7 @@ $ runqemu nographic
104	# Limitations	115	# Limitations
105		116
106	Few components do not build with clang, if you have a component to add to that list	117	Few components do not build with clang, if you have a component to add to that list
107	simply add it to conf/nonclangable.inc e.g.	118	simply add it to `conf/nonclangable.inc` e.g.
108		119
109	```shell	120	```shell
110	TOOLCHAIN_pn-<recipe> = "gcc"	121	TOOLCHAIN_pn-<recipe> = "gcc"
@@ -112,7 +123,7 @@ TOOLCHAIN_pn-<recipe> = "gcc"
112		123
113	and OE will start using gcc to cross compile that recipe.	124	and OE will start using gcc to cross compile that recipe.
114		125
115	And if a component does not build with libc++, you can add it to `conf/nonclangable.inc` e.g.	126	if a component does not build with libc++, you can add it to `conf/nonclangable.inc` e.g.
116		127
117	```shell	128	```shell
118	CXX_remove_pn-<recipe>_toolchain-clang = " -stdlib=libc++ "	129	CXX_remove_pn-<recipe>_toolchain-clang = " -stdlib=libc++ "