On Sat, 14 Oct 2017 01:51 am, Chris Angelico wrote: > On Sat, Oct 14, 2017 at 1:32 AM, Steve D'Aprano > <steve+pyt...@pearwood.info> wrote: >> It seems to me that you're not talking about ROM at all, but ordinary RAM. >> Then what do you mean by "read only"? A block of memory with a flag that >> says "unprivileged processes are prohibited from writing here"? >> >> (That's also not a rhetorical question.) > > When I first learned about Protected Mode (as defined by the Intel > 80386 and used in OS/2), there was a real concept of read-only RAM. > The program loader would fetch up the executable file (data on the > disk) and construct its segments: code, data, and BSS/stack. The data, > BSS, and stack all end up as a single segment (data is what comes > straight off the disk, BSS is all zeroes initially, and stack is > uninitialized initially, but ultimately they're all read/write), and > code is in its own segment. When control is handed to the new process, > its segment table grants it read/write access to the data/stack > segment, but read-only access to its code segment.
> Within that > process, the code really truly is read-only, unless some magic is > done. So... not actually read-only then? You have the program loader writing to it, repeatedly, every time you load a program. And even the unprivileged program itself can write to it, if it knows the correct incantation to use. So its more like Read/Write Memory, or as we normally call it, memory. You know, an awful lot of confusion could have been avoided if people had referred to write-protected memory as write-protected rather than read-only. -- Steve “Cheer up,” they said, “things could be worse.” So I cheered up, and sure enough, things got worse. -- https://mail.python.org/mailman/listinfo/python-list
