On 04-Dec-15 03:47, Alexander Neundorf wrote:
On Thursday, December 03, 2015 09:27:29 Ruslan Baratov via CMake wrote:
> On 03-Dec-15 04:34, Alexander Neundorf wrote:
> > On Wednesday, December 02, 2015 12:27:42 Ruslan Baratov wrote:
> > If RPATH was _designed_ to be patchable, tools could just do it,
> > instead of having to implement workarounds for longer strings. E.g.
> > the linker would support a command line argument how much space it
> > should reserve for the RPATH entry, or something like that.
>
> I think it's not possible. As far as I know there is no limitation for
> path size on Linux for example. Hence it's not possible to predict what
> size for path to library user want to use by setting RPATH.
More nitpicking about the meaning of "designed" ;-) :
CMake knows the length of the build RPATH and the length of the
install RPATH. Let's say the build RPATH has a length of 100, and the
install RPATH has a length of 150, it could, during linking, give the
build RPATH to the linker, and also something like --rpath-size=150,
and the linker would make the field for the RPATH 150 bytes big, so it
could be patched easly later on.
This is what I would consider the minimum support if it was "designed"
to be patched.
Instead cmake has to add 50 ":" at the end of the build RPATH. :-/
...
> > The idea above was only for solving the question "am I installed ?"
> > yes/no, not "where am I installed ?".
>
> Then I don't understand how it's planned to be used. I thought that in
> build directory you changing "$$$$_I_M_NOT_INSTALLED_$$$$" to
> "/path/to/build/directory" so resources can be found there, and on
> install you change it to "/path/to/install/directory". So my guess is
> not correct?
Nothing is planned, just some ideas.
The idea was, during install, to set the first byte of that special
string to '\0', and in the code you test whether the string is empty (
-> it has been patched, so it is installed) or not (still the original
"$$$$_I_M_NOT_INSTALLED_$$$$").
With that information, the developer can then do whatever he wants.
e.g. when not installed, search just in $CMAKE_BINARY_DIR (which could
be configured into some other string), and if installed, search in
some other way.
Will not work, just like I said compiler is smart enough to figure out
if the first char in string literal is '\0' or not. Just make some
testing: https://gist.github.com/ruslo/04d8993800ee78513d1c
The only one possibility to implement what you want I see in creating
new dynamic library (probably by CMake) with one literal:
// 3rd party library API
const char* path_to_install();
void parse_resources() {
const char* x = path_to_install();
assert(x != 0);
if (x[0] == '\0') {
// OK, can't be optimized since it's an external library
}
else {
// load resources
}
}
So CMake should create such library in build directory and then
re-create and install it with new string in install directory. Of course
if you move such library it will not work :) So still doesn't make sense
to me...
Ruslo
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