Symfony Profiler

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            "content": "<blockquote>\n<p>How does executing a program actually work?<\/p>\n<\/blockquote>\n<p>Way too long an answer for a lemmy post<\/p>\n<blockquote>\n<p>It has an executable flag, but what actually happens in the OS when it encounters a file with an executable file?<\/p>\n<\/blockquote>\n<p>Depends on OS. Linux will look at the first bytes of the file, either see (ASCII) <code>#!<\/code> (called a shebang) or ELF magic, then call the appropriate interpreter with the executable as an argument. When executing e.g. python, it\u2019s going to call <code>\/usr\/bin\/env<\/code> with parameters <code>python<\/code> and the file name because the shebang was <code>#!\/usr\/bin\/env python<\/code>.<\/p>\n<blockquote>\n<p>How does it know to execute \u201cmain\u201d?<\/p>\n<\/blockquote>\n<p>Compiled C programs are ELF so it will go through the ELF header, figure out which <code>ld.so<\/code> to use, then start that so that it will find all the libraries, resolve all dynamic symbols, then do some bookkeeping, and jump to <code>_start<\/code>.<\/p>\n<blockquote>\n<p>Is it possible to have a library that can be called and also executed like a program?<\/p>\n<\/blockquote>\n<p>Absolutely. <a href=\"https:\/\/man7.org\/linux\/man-pages\/man8\/ld.so.8.html\" rel=\"nofollow\"><code>ld.so<\/code> is an example of that.<\/a><\/p>\n<p>If you want to start looking at the innards like that I would suggest starting <a href=\"https:\/\/jameshfisher.com\/2018\/03\/10\/linux-assembly-hello-world\/\" rel=\"nofollow\">here<\/a>: Hello world in assembly. Note the absence of a <code>main<\/code> function, the symbol the kernel actually invokes is <code>_start<\/code>, the setup necessary to call a C <code>main<\/code> is done by <code>libc.so<\/code>. Don\u2019t try to understand GNU\u2019s libc it\u2019s full of hystarical raisins I would suggest <a href=\"https:\/\/musl.libc.org\/\" rel=\"nofollow\">musl<\/a>.<\/p>\n",
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                "content": ">  How does executing a program actually work?\n\nWay too long an answer for a lemmy post\n\n> It has an executable flag, but what actually happens in the OS when it encounters a file with an executable file? \n\nDepends on OS. Linux will look at the first bytes of the file, either see (ASCII) `#!` (called a shebang) or ELF magic, then call the appropriate interpreter with the executable as an argument. When executing e.g. python, it's going to call `\/usr\/bin\/env` with parameters `python` and the file name because the shebang was `#!\/usr\/bin\/env python`.\n\n> How does it know to execute \u201cmain\u201d?\n\nCompiled C programs are ELF so it will go through the ELF header, figure out which `ld.so` to use, then start that so that it will find all the libraries, resolve all dynamic symbols, then do some bookkeeping, and jump to `_start`.\n\n>  Is it possible to have a library that can be called and also executed like a program?\n\nAbsolutely. [`ld.so` is an example of that.](https:\/\/man7.org\/linux\/man-pages\/man8\/ld.so.8.html)\n\nIf you want to start looking at the innards like that I would suggest starting [here](https:\/\/jameshfisher.com\/2018\/03\/10\/linux-assembly-hello-world\/): Hello world in assembly. Note the absence of a `main` function, the symbol the kernel actually invokes is `_start`, the setup necessary to call a C `main` is done by `libc.so`. Don't try to understand GNU's libc it's full of hystarical raisins I would suggest [musl](https:\/\/musl.libc.org\/).\n\n",
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